Keystroke values are the values returned by the GetKey command to indicate which button was pressed.
The value ends up to be a 2 or 3 digit number with the row number (starting from the top) being the 1st (or 2nd, in the case of row 10) number and the column number being the 2nd number.
Y= is 11
Enter is 105
2nd is 21, etc.
Keystroke values are more complex in TI-89 since TI-89-BASIC gives support to 2ND, 3RD, Alpha and ↑ keystrokes.