Variable names can have between 1 and 8 characters. Numbers and letters are legitimate, including Greek letters, accented letters, and international characters (all accessible through the CHAR menu, 2nd +. You can also get to the Greek letters via diamond G on the TI-992+ and diamond ( on the TI-89. Check the owner's manual on this, as not all Greek letters are available, and the procedure isn't obvious.)

Exceptions: you can't use p (pi), and the first character in a name can't be a digit.

Variable types indicate what sort of thing is stored at that memory location. The codes are the abbreviations the calculator uses in the VAR-LINK screen.

• ASM:    Assembly-language programs. Not even your owner's manual says much about these. Check the TI web site.
• DATA:    A data variable is a collection of lists, something like the entries in a spreadsheet. You work with them in the Data/Matrix editor.
• EXPR:    Expressions are numbers, variables (in the mathematical sense), outputs of functions (like sin(x) or f(2)), or combinations of these. Essentially, an expression is anything that isn't something else.
• FIG:    Used in the Geometry module, which is a free download from TI, but not included with the calculator.
• FUNC:    Functions take inputs and produce outputs. The easiest way to define your own functions is with the STORE command, or its equivalent, the Define command. You can also use the Program Editor (accessible via the APPS key) to create functions, including functions with multiple lines. See your owner's manual for details.
• GDB:    Graph databases store the information on the GRAPH screen so you can recover a screen later.
• LIST:    A list is a sequence of up to 999 numbers, other expressions, or character strings (or all of theses). In the Data/Matrix editor, lists appear as a column of cell entries (without empty cells). On the HOME screen, the items in a list appear in braces ( { } )separated by commas.
• MAC:    These are macros used in Geometry sessions. The TI-92 included a Geometry module, but not the TI-92+ or the TI-89. See FIG, above.
• MAT:    A matrix is a rectangular array of numbers or other expressions. Vectors are stored as matrices with only one row.
• PIC:    Pictures of graphs are different from graphs. A PIC variable contains only the pixel information, while a GDB variable includes all the information necessary to reconstruct the graph.
• PRGM:    Programs are similar to functions, but more versatile. Programs take over your calculator while they run, though, and don't produce output that you can use on the command line of the HOME screen.
• STR:    Strings are sequences of characters enclosed in quotation marks. (You can get quotation marks from the CATALOG, before the A's, or more easily from the keyboard: 2nd L on the TI-92+ and 2nd 1 on the TI-89.)
• TEXT:    Text variables hold output from the Text Editor, accessible via the APPS key. You can store the contents of the history area of the HOME screen as a text variable, so you can reconstruct calculations you performed in the past.

On the HOME screen, you can store information in variables with the STO command or the Define command, and you can remove information from variables with the delvar command. You can also delete all the variables with one-letter names (a-z) with the NewProb command.
 

System variables are reserved storage locations that the calculator uses for internal purposes. You look at, but not change, the list of system variables on the VAR-LINK screen. For example, xmin and xmax, defined on the WINDOW screen, are system variables. System variables are normally available for you to use on the command line of the HOME screen and in functions and programs.
 

The MEM screen (2nd 6) will tell you how much total memory each type of variable is using. The VAR-LINK screen will tell you what variables you've stored and how big each one is.

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