Figure 3.1. Main Window

The main window provides a menu bar, the expression entry, the result display and a calculator keypad, history and conversion view (see the section called “Conversion”) which can be shown/hidden by clicking on Keypad, History and Conversion, respectively. When non-default options for the interpretation of expressions have been selected, the choice will be indicated in a small status area below the expression entry, to the right (click to change these choices).

The expression entry is the most important part of the Qalculate! user interface. The normal calculation procedure in Qalculate! is to type in a mathematical expression (e.g. “5 + 5”) and press Enter (or click =). The result (“10”) is then displayed below the expression entry in the result display.

The icon in the upper right corner of the expression entry changes function depending on the current status. While editing the expression an equals sign is shown. When the icon is clicked the expression will be calculated. If this results in an error or a warning, the corresponding icon will be displayed instead, and if this is clicked, or if the pointer is placed over it, the error/warning text will be shown. If no error or warning is triggered, activation of the icon will instead clear the expression entry. No icon is shown when the expression is empty.

Figure 3.2. Completion

Qalculate! helps out with the expression by giving a list of possible endings to words representing functions, variables and units. Titles, and countries for currencies, will also be searched, but any matches will be placed at the end of the list. The list will narrow with each letter typed. Select an item in the list and the name will be completed. If a function was selected, parenthesis will be added and the position moved for immediate entry of arguments. Completion can be configured from the context menu, or in more detail, from the preferences dialog.

As the expression is typed in, the area directly below the expression entry, to the left, will show useful information. By default the calculator's interpretation of the expression is shown (e.g. “5 × meter” for “5m”). The interpretation will be displayed in red (configurable) if there are errors in the expression or in blue for lesser errors (for example too many arguments in a function). If the last typed-in text represents a function and arguments are about to be entered, the function's name and its arguments will be displayed. The first argument in the information text is highlighted and includes information about its type and restrictions and when an argument has been entered, the next will be highlighted.

After execution of an expression, the whole expression will be marked. This normally means that if something new is entered, the old expression will be overwritten. If, however, an operator (+, −, ×, /, ^) is entered first, the old expression will instead be the target of action. The operator will then apply to the whole expression, which is put in parenthesis. This works on all marked ranges, meaning that this way an expression can conveniently be put in parenthesis. Functions set the selection as their first argument.

The Page Up and Page Down keys will access previously entered expressions. With focus in the expression entry, Page Up traverses backwards in the expression history and Page Down forward. The Up and Down can also be used for the same purpose when the completion list is not shown.

Although the expression entry can display multiple lines of text, the Enter key does not insert a line feed. New lines are automatically created when needed.

The expression entry also accepts commands, preceded be “/”. These commands are the same as in the command line program, qalc.

The font used for the expression entry can be selected in the preferences dialog (Edit → Preferences).

Right-click in the expression entry to open a context menu, with general text editing options as well as selection of parsing modes (including number base), and menu items which open dialogs for insertion of vectors, matrices, or dates.

The result of calculations is displayed in the open area below the expression entry. The font used for the result display can be selected in the preferences dialog (Edit → Preferences). Use of Unicode signs can be turned off in the same dialog. Otherwise Qalculate! will try to make the result as fancy as possible and print π for pi, √ for sqrt, € for euro, and so on. Information about customization of the mathematical result output is available in Chapter 5, Calculator Modes.

In front of the result an equals or approximately equals sign is shown. This indicates whether Qalculate! was able to calculate/display the result exact or only approximate, in the current mode.

The result display has a context menu, which pops up when clicking with the right button anywhere in the field. This menu provides a subset of the display alternatives from the mode menu (Table 3.7, “Mode Menu”) and some actions from the edit menu (Table 3.6, “Edit Menu”). See more info in Chapter 5, Calculator Modes.

If you hold the pointer over the result area a tooltip will show the text representation of the result. To make it more obvious what the result means, abbreviations and implicit multiplication are not used here, and excessive parentheses are shown.

To copy the result, either select Edit → Copy Result, press Ctrl+Alt+C, or copy the text from the history window.

The keypad provides access to a simple traditional number pad and as well as more advanced functionality.

Figure 3.3. Keypad

Click on the padlock icon to enable/disable persistent keypad, which makes it possible to display the keypad and the history simultaneously (the keypad view will be independent of the other views).

The top buttons (from left to right) switches between the general keypad and the programming keypad (affects the buttons on the left side, see Table 3.3, “Programming Keypad”), switches between exact and approximate calculation, changes rational number form, selects display mode and selects number base in result (see Chapter 5, Calculator Modes).

The buttons below are separated in two areas. The buttons on the right inserts basic numbers and operators, while most of the buttons to the left inserts or applies mathematical functions to the expression. All buttons on the left is paired with buttons, with downward arrows, that opens a menu with related functionality (generally more mathematical functions).

Most of buttons to the right will do something different depending on which button on the pointing device (mouse) that is clicked (for details see the table below; all actions are displayed as tooltips when holding the pointer over a button). Button press and hold on a button (for approximately half a second) will generally perform the same action as right-click. Right-click or long press on the buttons to the left will open the associated menu.

Selected/marked text in the expression entry is handled in different ways depending on the type of keypad button used. Numbers, variables and units will replace the selected text.

Operators will be placed after any selected text (except bitwise and logical NOT which is placed in front of the selection), which is put in parentheses. This, together with the fact that recently calculated expressions are automatically selected in the entry, means that if you click 5, 9, +, 2, =, × and 2 in order, the result expression is “(59 + 2) × 2”. In RPN mode the operators acts on the top two registers in the stack.

The mathematical functions accessed using keypad buttons (and menus) behave differently depending on the current edited expression. If the cursor is at the end of the expression and there is no operator or parenthesis immediately to left of the cursor (at the end of expression), the whole expression is used as function argument and the expression is immediately calculated using the function (if you type “5 + 2” and then click sin, “sin(5 + 2)” will be calculated). If text in the expression is selected, the selection will be used as the function argument. If the whole expression was selected the resulting expression will immediately be calculated. Functions that requires more than one argument do not follow these rules and in many cases opens a separate dialog for argument input. In RPN mode the function will always be applied to the register(s) at the top of stack, if the current expression is empty and there are enough registers for functions that require more one argument.

All actions and labels of the buttons on the right can be customized using Edit → Customize Keypad Buttons (it is also possible to add additional columns of buttons). The default buttons, and associated actions, are listed below.

DEL deletes one character to the right or, if the cursor is at the end of the expression, to the left of the cursor (right-click always deletes the character to the left of the cursor). Long press on the button will continuously delete.

EXP inserts the shorthand notation (E or e) for ten raised to the power of x. This only applies to digits (“2E6” equals “2 × 10^6”, “xEy ≠ x × 10^y”). If whole or part of the current expression is selected, “×10^” will instead be inserted after the wrapped selection. If current input base is not 10, than the selected number base will be used as base (e.g. “×16^” for hexadecimal input).

ANS inserts the first answer variable. This variable always contains the last calculated result. This will be updated after each calculation (unlike when using the answer() function with a positive argument).

The “(x)” button (Ctrl+() places opening and closing parentheses around the selected text in the expression entry. If no text is selected either the expression to the right of the cursor (if the cursor is at the beginning of the expression or if there is an operator or left parenthesis to the left of the cursor) or to the left of the cursor is put inside parentheses. If the expression is empty, as well as in some other cases (to avoid broken expression), empty parentheses are inserted.

The arrow buttons works a bit differently than the other. The direction of the action will depend on which half of the button that is pressed (the right side of the button, with the arrow pointing to the right, will move the insert cursor when step forward). Long press on the button will continuously move the cursor (or continuously cycle through the expression history).

The characters used as decimal point and argument separator varies between different locales. The argument separator is used for separation of arguments to functions that takes more than one argument.

Below follows a list of the buttons on the left side (including their menus and associated actions), from left the right, top to bottom.

Figure 3.4. Programming keypad

The buttons on the left side can be replaced (using the top left button or Ctrl+P) by a set of buttons for quick access to functions particularly useful for programmers. In place of the menus over the keypad, the current result will be shown in binary, octal, decimal and hexadecimal number bases. The buttons are listed below, from left to right, top to bottom.

The history view provides access to previous calculation results (50 rows are reloaded on restart). Previous expressions and results, as well as errors and warnings, are listed. The text of one or multiple entries can be copied to the clipboard using the Copy button to the right of the list.

Figure 3.5. Calculation History

Double click an item in the history list or use the Value or the Text button to paste the selected value or expression into the expression entry. The Value button inserts the actual value, using the answer() and expression() functions (for results and parsed expressions, respectively) with the current history index (indicated in the left column of the list), as argument, instead of the text (which might be inexact and is not guaranteed to be parsed correctly). This is not possible for the history entries of previous sessions. When an item is double clicked the actual value is used for results, but the text for expressions, allowing editing of the expression.

To the right of the list are also buttons for mathematical operations. These act on the selected history items (the + will calculate the sum of the selected values, while the − will calculated the difference between the first, uppermost, selected value and the rest, in order). If no value is marked the sign for the operator will be inserted into the expression entry (as the buttons on the keypad). If only one item is selected the buttons also use the current expression (the + button will append “+ [value]” to the current expression). The square root button will however only act on single values. When persistent keypad is active, the corresponding buttons on the right side of the keypad provide the same functionality.

Additional actions are available in the context menu of the history list. This includes options to copy the full text of one or multiple entries, search the history, delete or move entries, to clear the whole list, and to bookmark and/or protect entries from deletion when the list becomes too long or is cleared.

It is possible to minimize the footprint of the calculator window using File → Minimal Window or Ctrl+Space. This will hide everything but the expression entry and the equals button. The window is expanded to reveal to result, but the result display stays hidden while empty. Restore the window using the keyboard shortcut or the icon in lower right corner of the expression entry.

Figure 3.6. Minimal Window

The menus in the menu bar provides access to most of the functionality of Qalculate!. Their contents are listed and described below.

The variables, functions, and units windows provide a structural way of working with variables, functions and units (collectively referred to as objects). The windows for the three different objects are essentially similar. They can be opened from the edit menu, or using Ctrl+M, Ctrl+F and Ctrl+U for variables, functions and units respectively.

Figure 3.7. Variable Manager

To the left is a category tree and beside that is a list of all objects in the selected category, including all subcategories. Objects without a category are put under “Uncategorized”. Objects created by the user can also be found under the category “User variables”, “User functions”, and “User units”, shown at the top of the list. Deactivated objects are only found in the “Inactive” top category. Below the categories and objects lists, a description of the selected object is shown.

The buttons on the right work on the selected object in the list. New opens a dialog for creation of a new object, while Edit opens the same dialog to edit the selected unit. Delete removes the object and (De)activate toggles recognition in expressions on/off. Insert in the variables and units windows adds the object to the current expression, while Calculate in the functions window opens a dialog for entering arguments and provides options for insertion of the function or direct calculation. The unit manager provide an additional button for conversion of the current result, the variable manager a button for export to a data file, and the function manager a button for applying functions with a single argument directly to the current expression.

Figure 3.8. Function Manager

The function manager has a description box at the bottom, which shows the syntax, description and arguments of the selected function.

Figure 3.9. Unit Manager

The unit manager has an area for quick conversion between units. This converts between the selected unit in the list and the selected unit in the menu. Both the menu and the list filters the units as you type. Units are converted by specification of a quantity, in the entry next to the unit to convert from, followed by Enter.

For more information about variables, functions and units, see Chapter 7, Variables, Chapter 8, Functions and Chapter 9, Units.

The number bases dialog, accessible from the File Menu, is an efficient and convenient tool for conversion between binary, octal, decimal, duodecimal, hexadecimal and Roman numbers. This dialog contains entries for each number base. When a number is typed in any of the entries, the others are automatically updated to display the current number in their format. Numbers, or expressions, entered follow the same rules as expressions in the main expression entry.

Figure 3.10. Convert Number Bases Dialog

In Qalculate! mathematical entities, such as numbers and variables, are referred to as objects. The recognized object types are listed below.

To avoid confusion, functions, units, variables and unknown variables can independently be disabled.

Variables, functions and units are all accessible in the menus and in the variable, function and unit managers, If their names are not remembered. Functions accessed this way have some extra conveniences. If the function has at least one argument, a dialog will pop up where arguments can be entered and a description of the function and its arguments is available.

Qalculate! can handle most commonly used symbols for certain variables, functions and units, even though most are difficult to find on a keyboard. These include π for pi, √ for sqrt, € for euro, and so on. Most importantly it is possible to copy these symbols when used in the result.

For more information about variables, functions and units, see Chapter 7, Variables, Chapter 8, Functions and Chapter 9, Units.

The following operators are defined in Qalculate! and may be used in expressions. Word operators (such as AND) must be surrounded by space (e.g. “5 mod 2”, not “5mod2”.

The multiplication sign can generally be left out. This is not true for numbers (“5(5) = 25” but “5 5 = 55”). Expressions can also generally be written with or without spaces with the same result (“2xsin(2)” equals “2 x sin(2)” which equals “2 × x × sin(2)”), but be careful. The vast number of functions and units means that without separating spaces, the result might not be obvious. To avoid confusion Qalculate! can limit the use of implicit multiplication (Mode → Limit Implicit Multiplication), so that space, operator or parenthesis must be put between functions, units and variables (in this mode “esqrt(5)” does not equal “e × sqrt(5)”). Also note that unit prefixes must be put immediately before the unit, to be interpreted as prefixes (“5 mm = 0.005 m”, but “5 m m = 5m^2”). You can see how the expression was interpreted in the history window.

Usually, mathematical expressions are written as normally expected. Standard operator precedence apply. Expressions are evaluated according to the following priorities:

The evaluation of short/implicit multiplication, without any multiplication sign (e.g. “5x”, “5(2+3)”), differs depending on the parsing mode. In the conventional mode implicit multiplication does not differ from explicit multiplication (“12/2(1+2) = 12/2×3 = 18”, “5x/5y = 5 × x/5 × y = xy”). In the “parse implicit multiplication first” mode, implicit multiplication is parsed before explicit multiplication (“12/2(1+2) = 12/(2 × 3) = 2”, “5x/5y = (5 × x)/(5 × y) = x/y”). The default adaptive mode works as the “parse implicit multiplication first” mode, unless spaces are found (“1/5x = 1/(5 × x)”, but “1/5 x = (1/5) × x”). In the adaptive mode unit expressions are parsed separately (“5 m/5 m/s = (5 × m)/(5 × (m/s)) = 1 s”). Function arguments without parentheses are an exception, where implicit multiplication in front of variables and units is parsed first regardless of mode (“sqrt 2x = sqrt(2x)”).

If the limit implicit multiplication option is activated, the use of implicit multiplication when parsing expressions and displaying results will be limited to avoid confusion. For example, if this mode is not activated and “integrte(5x)” is accidently typed instead of “integrate(5x)”, the expression is interpreted as “int(e × e × (5 × x) × gr × t)” (displayed in history window). The result will then without any error be “int(2.3940139x × km^2)” instead of “2.5x^2”. If limit implicit multiplication is activated, the mistyped expression would instead show an error telling that “integrte” is not a valid variable, function or unit (unless unknowns is enabled in which case the result will be “5 "integrate" × x”). When implicit multiplication is limited, variables, functions and units must be separated by a space, operator or parenthesis (“xy” does not equal “x × y”).

In addition there are two special parsing modes — RPN syntax (for details see the section called “The RPN Mode”) and chain syntax. The chain syntax interprets expressions in a manner similar to the immediate execution mode of a traditional calculator. Instead of using the standard order of operations, the expression is simply calculated from left to right (e.g. “1 + 2 × 3 = (1 + 2) × 3 = 9” instead of “1 + 2 × 3 = 1 + (2 × 3) = 7”). Functions, with a single argument, apply to the value immediate to the left of the function name (e.g. “1 + 2 sin = 1 + sin(2)”), unless parentheses are used.

Putting “ to ” (or a right arrow, e.g. “->” but not “>”) followed by an expression at the end of the mathematical expression is mainly used for unit conversion (see the section called “Conversion”). There are however also some convenient commands that can be typed after “ to ”. Here is a list of possible “to” values:

If “to” is not preceded by an expression, the previous result will be converted.

Similarly “where” (or alternatively “/.”) can be used at the end (but before “to”), for variable assignments, function replacements, etc. (e.g. “x+y where x=1 and y=2”, “x^2=4 where x>0”, and “sin(5) where sin()=cos()”). Variables assignments can also be placed before the expression, separated by comma, e.g. “x=1, y=2, x+y”, but this syntax is more strict.

Note that “to” and “where” can only be applied to the whole expression. Everything before the operator is always treated as the expression to convert (or apply replacement to), and everything after as the conversion/replacement expression, regardless of any parentheses.

The Reverse Polish Notation mode can be activated from Mode → RPN Mode, Ctrl+R or from the context menu of the expression entry. For details about what Reverse Polish Notation is and how it generally works, see for example the RPN article at Wikipedia.

Central to the RPN mode is the stack, a list of registers/values that is operated on by functions and operators. The stack has a variable number of registers which can hold an unlimited number of values. The stack size is dynamically changed when a new value is added and the first value on the stack is shown in the result display. Mathematical operators such as plus and minus then operates on the first two, last added, values on the stack. The second value is changed with input from the first value. For example, the minus operator subtracts the first value from the second.

For example, 5 ENTER 3 + 2 / adds 5 to the stack, then adds 3 to the stack and moves 5 down a step and adds 3 to 5. The first value, 3, is removed from the stack and the value left is 8. Then 2 is added to the stack and 8 is divided by 2, resulting in 4. This would in a single expression with non-RPN (infix) syntax be entered as “(5 + 3)/2”.

Functions operate on the top values of the stack. Functions which require multiply arguments, fill the arguments in reversed order from the top (e.g. 5 ENTER 2 ENTER rem equals “rem(5, 2)”). Functions with a vector argument use all stack registers (unless the top value is a vector). This is quite useful for statistical functions (e.g. 5 ENTER 2 ENTER 3 ENTER 4 ENTER harmmean calculates the harmonic mean of 5, 2, 3, and 4 and leaves the result, 3.1169, as the only value on the stack).

When the RPN stack is enabled, full expressions can still be entered (you can add e.g. “5x + 3 + 23 + sin(2)” directly to the stack). The buttons on the keypad do not insert operators and functions in the expression entry, but instead apply them to the stack. This is also true for the keys on the keyboard, unless deactivated in the preferences (Edit → Preferences, Use only keypad keys for RPN). Enter calculates the current expression and adds it to the stack (calculated mathematical expressions are automatically added to the stack when the RPN stack is enabled). If the expression entry is not empty when applying an operator or function to the stack, the expression is first calculated and added to the stack. If the expression only contains an operator or a single function without arguments, the operator/function is applied to the stack.

Figure 5.1. RPN Mode

The RPN mode adds a third page to the main window, for display and manipulation of the values on the stack. This shows a list of values on the stack, with the last added value on the top.

On the right are buttons for manipulation of the stack. The buttons move the selected value up (Ctrl+Up) or down (Ctrl+Down), move it to the top (Ctrl+Right), copy it (Ctrl+Shift+C), edit it, or remove it (Ctrl+Delete), in order. If no stack row is selected, the up and down buttons rotates the stack, the swap button swaps the places of the first and second value and the copy and delete buttons acts on the top value of the stack. The button between copy and delete enters the top value from before the last numeric operation (Ctrl+Left). The last button removes all values from the stack (Ctrl+Shift+Delete).

On the left are buttons for applying mathematical operations to the stack. The top left buttons applies addition, subtraction, multiplication, division, and exponentiation to the top two values. If only one value is available addition, multiplication, and exponentiation uses this value twice, while the subtraction button negates the value and the division button calculates the reciprocal. The buttons below negates the top value, calculates the reciprocal, and calculates the square root of the top value. The last button calculates the sum of all values on the stack. Changes in the display of results only affects the first value on the stack.

Reverse Polish Notation can also be used directly in expression. This can be activated or deactivated separately from the RPN stack (Mode → Parsing Mode → RPN Syntax). When using RPN syntax, a temporary stack, separate from the previously mentioned stack, is created from the contents of each mathematical expression entered. To calculate “(5 + 3)/2”, as in the example above, with RPN syntax you should enter the expression “5 3 + 2 /”. Instead of actually pressing enter on the keyboard, each separate value on the stack is separated by a blank space.

Figure 7.1. Store Result

The easiest way to create a known variable is to store the current result. This can be done by clicking the STO button or selecting File → Store Result.... Type a name for the variable in the dialog that pops up. The name is used in expressions (e.g. “var_1 + 5” if the variable is named “var_1”). Temporary variables (placed in the “Temporary” category) disappear when Qalculate! is closed.

Known variables can also be created from scratch by selecting File → New → Variable or by clicking New in the variable manager. The value is entered in the text field below the name. Any mathematical expression is allowed as value (e.g. “π m” or “sin(2) + ln(3)”).

It is possible to specify multiple names, and various properties of these names, by clicking the icon on the right side of the name field.

The second page of the dialog provides fields for entry of descriptive name (shown as title in menus), category, and description.

Figure 7.2. New Variable

Alternatively values can be stored in variables using the save() function, or the associated “:=”/“=” operators (e.g. “save(v1, 5)” or “v1:=5”, “save(v1, ln(5)+2,,,1)” or “v1=ln(5)+2”).

The dialog for creation of unknown variables is accessed by selecting File → New → Unknown Variable. Instead of a value, an assumed type and sign can then be selected.

Edit a variable by clicking Edit in the variable manager, or using the context menu (right-click) of the corresponding menu item in the menu of the STO.

The special MR (= right-click) variable is updated using the classic MC (AC right-click), MS ((= middle-click), M+ (+ right-click), and M− (DEL middle-click) operations.

Vectors and matrices are most effectively used stored in a variable. Qalculate! provides separate tools for these variables. They use a different dialog, where each element can be edited separately as in a spreadsheet. As with other variables, click Edit in the variable manager to edit a matrix/vector variable, but to create a new, select File → New → Matrix or File → New → Vector.

Figure 7.3. Matrix/Vector Edit Dialog

In this dialog, name, category and descriptive name are typed in as usual, but instead of a single value field, multiple values are entered using a table. The number of rows and columns are selected using the controls above the table. In a vector this only determines how many cells that are shown in the table and empty cells will be ignored. For matrices, each cell in the table is an element in the matrix.

Matrices and vectors can also be loaded from data files. These files must be plain text files with values organized in separated rows and columns. Select File → Import CSV File... and a dialog window pops up. First select the file to import and then specify whether it shall be imported as a matrix or vectors. A name, descriptive name and category can optionally be typed in. If the name field is empty, the file name will be used instead. After that, the row in the file where the data starts should be specified, as well as whether this first row contains column headings. Finally the delimiter, used to separate columns in the file, must be selected. Click OK and variables will be generated from the file. If vectors are to be generated and the file contains more than one column, the name will be used as a subcategory and each variable will add the column heading (or “Column 1”, “Column 2”, ...) to the name and the descriptive name.

Figure 7.4. Import CSV Dialog

The load() function can be used to access a CSV file directly in an expression. The reversed action is also available with export(), or the dialog accessed with File → Export CSV File... or from the variable manager.

Here the main function categories and some of their members are described, to give an overview of available functions. For information about separate functions and a complete list of all available functions see Appendix A, Function List or the function manager.

Functions are a bit more complex than variables, but can nevertheless be relatively easily created. Select File → New → Function, or click the f(x) on the keypad or New in the function manager and a function edit dialog pops up.

The function edit dialog is divided in three pages, where the first page contains the only required properties — name and an expression. x, y and z with or without (default) a backslash are used as argument placeholders in the expression.

Figure 8.2. Function Edit Dialog

First enter a name, used to reference the function in an expression. Then enter an expression below.

The expression of a function is basically a normal expression with placeholders for arguments. The expression “x^4” creates a function which calculates the fourth power of a single argument. If you name it for example “sqsq”, “sqsq(2)” will calculate “2^4”.

The argument placeholders consist of a backslash and a letter — x, y, z for the 1st, 2nd and 3rd arguments and a to u for argument 4 to 24. The backslash can however be omitted, but avoids any possible conflict with existing variables, units and functions used in the expression. The argument symbols are replaced by entered arguments when a function is calculated. They also decide the number of arguments that a function requires. For example the function for triangle area (“base × height / 2”) has the name triangle and the expression “(\x × \y)/2”, which gives that “triangle(2, 3)” equals “(2 × 3) / 2” and returns “3” as result. An argument can be used more than one time and all arguments must not necessarily be in order in the expression.

Additionally, optional arguments can be put in the expression with upper-case (X, Y, Z, ...) instead of lower-case letters (x, y, z, ...). The default value should be put in curly brackets after the letter (e.g. “\X{2}”). The default value may be omitted and is then zero. All additional arguments after an optional argument must also be optional.

Figure 8.3. Function Edit Dialog

A required condition, sub-functions, and argument definitions can optionally be specified in the second page (“Details”).

The condition specifies an expression which must evaluate true before the function is calculated. This follows the same conventions as function expressions. For example, if the value of the second argument must be higher than the first, “\y > \x” may be entered as a condition.

Sub-functions can be useful for complex functions, they use the same syntax as the main expression, and are references using a backslash followed by a number (e.g. “\1” for the first sub-function). The sub-function can be inserted in the main expression as a precalculated value or intact (meaning that the subfunction might be recalculated for each occurrence in the main expression).

Name, type, and required conditions can be specified for each argument.

The third page allows entering of category, descriptive name (shown as title in menus) and description. The function can also be hidden from menus with the corresponding check box, which can be useful for functions only used in other functions.

Global, system-wide functions can not actually be changed by the user, but if one of these functions is edited, they are deactivated and seemingly replaced by a new function. Some functions are however hard-coded and cannot be changed by the user. Once the user function is removed or deactivated the original function is automatically reactivated.

Among units, Qalculate! has support for currencies with up-to-date exchange rates. Currencies are normally referenced with the standard three letter code due to name clashes, but a number of currency unit can also be accessed through their regular name and symbol. U.S. dollars can, for example, be referenced both as USD and dollar/dollars or the $ symbol, unless the same name and/or symbol are used by the local currency.

The exchange rates can be updated manually using File → Update Exchange Rates, or automatically at specific intervals (by default once every week, but this can be changed in the preferences dialog), when needed (when currencies are converted).

Expressions can be converted to a specific unit directly in the expression entry with the “to” operator (right arrows, including “->” are also supported), which converts the left-hand expression (or the previous result) to a specified unit (e.g. “5 feet + 2 inches to cm” converts the result of “5 feet + 2 inches” to centimeters). Unit expressions may contain units, prefixes, exponents, multiplication and division. By default, no prefix will be added to units typed without prefix, but this behavior can be modified by putting a question mark in front of the unit expression (“6 561 ft to m ≈ 2000 m” but “6 561 ft to ?m ≈ 2 km”). Type “to optimal” to get optimal unit, “to base” for base units, or “to mixed” to force the use of mixed units (see below). Note that the conversion is always applied to the whole left-hand expression, ignoring any unmatched parentheses. The “to” operator can also be used for other types of result transformations (see the section called “The “to” (and “where”) operators”).

Alternatively the unit conversion view can be used. It is opened using Conversion, Ctrl+O, Edit → Convert To Unit Expression... or Ctrl+T (the last two options moves the focus to the unit expression entry). Enter a unit expression in the text entry and press Enter (or click Convert), or select a unit from the list. An appropriate unit category will automatically be selected from units in the current result. If Continuous expression is checked subsequent results will automatically be converted (if the conversion view is open), and if Add prefix is checked the optimal prefix will be set for unit expressions without any prefix. A unit can be inserted directly into the expression entry from the list using middle click or the context menu.

Figure 9.1. Unit Conversion View

The result context menu and the menu associated with the to (x ➞) keypad button also provides a list of units for conversion.

The final way to convert the result to another unit is to use Edit → Convert To Unit menu or to press Convert Result in the unit manager, which also provides quick conversion of a value between two selected units. Edit → Set Prefix can be used to select a prefix.

It is also possible to let Qalculate! automagically convert the result to appropriate units with Edit → Convert To Optimal Unit or Edit → Convert To Base Units (or the corresponding options in the result context menu). If instead the corresponding choice is selected from Mode+Unit Display (or the result context menu), each result will automatically be converted until the choice is deactivated (Mode+Unit Display → No Automatic Conversion).

By default (controlled by Mode → Unit Display → Convert To Mixed Units) certain units, such as time units and many imperial/U.S. customary units, are automatically converted to mixed units (e.g. “60.2 minutes = 1 hour to 12 seconds”). When explicitly converting to a specific unit the integer value of the selected unit is preserved (“1.51 h to min = 90 min + 36 s”) and mixed units is not used if otherwise the unit would not be present in the result (“6 in to ft = 0.5 ft”). This behavior can be modified by prepending the unit with a plus or minus sign (e.g. “174 cm to +in ≈ 5 ft + 8,5 in”, “1.51 h to -min = 90.6 min”).

There are three different unit classes in Qalculate! — base units, named derived units, and (unnamed) derived units. Base units are standard units that form the basis for all other units. Meters and seconds are typical base units. Derived units are defined in relation to other units. Named derived units are defined in relation to a single other unit, with an optional exponent (e.g. hour is defined as a named derived unit that equals 60 minutes which in turn is defined in relation to seconds). Unnamed derived units are defined by a unit expression with one or multiple units (e.g. “J/s”). They are primarily useful as basis for named derived units (e.g. W = J/s), and for simplified conversion and entry of the specified unit expression.

Select File → New → Unit, or click New in the unit manager, and the unit edit dialog pops up.

Figure 9.2. Unit Edit Dialog (General)

Base units and named derived units normally have three different name forms defined for use in expressions — abbreviation (e.g. “m”), singular (“meter”) and plural (“meters”). Unnamed derived units only have an internal name, which is used to reference the unit in definitions of other units, but which should not be used in mathematical expressions.

In addition category and descriptive name can be specified to keep the units well organized. A unit can be hidden from unit menus with the corresponding check box (this is primarily useful for some unnamed derived units which are only defined as basis for named derived units).

Depending on the unit class, different elements in the relation page of the dialog will be enabled.

Figure 9.3. Unit Edit Dialog (Relation)

For named derived units, base unit, exponent and relation must all be specified (although the exponent and relation may both be left as “1”). The base unit can be of any unit class and it is recommended that named derived units are defined in relation to the closest unit (e.g. 1 ft = 3 hands, 1 hand = 4 in, and 1 in = 0.0254 m). The relation is usually just a number that tells how large quantity of the base unit is needed to get the derived unit (derived unit = relation × base unit^exponent).

It is possible to create units with non-linear relation to the base unit. Replace the factor with “\x” and the exponent with “\y” (e.g. “\x + 273.15” for degrees Celsius with Kelvin as base unit). For non-linear relations the reverse relation (for conversion back from the base unit) should also be specified (“\x - 273.15” for degrees Celsius).

Base unit mixing can be enabled (by default) for named derived units. This is used for units such as feet and minutes, which are often combined with other units instead of using decimals (e.g. “5.25 ft = 5 ft + 3 in”, “250 s = 4 min + 10 s”). This behavior can be fine-tuned using the priority and minimum base unit number properties.

For unnamed derived units a unit expression, with one or multiple units, must be specified in the base units field. This expressions may only contain units, prefixes, exponents, multiplication and division (e.g. “km/h”).