FREEVAR is a numerical read-only system variable which indicates how many new variable names may be used before running out of memory.
The Petit Computer system can handle up to 2048 variable identifiers. Every time an array is declared, or a variable is written to (or read from!) that has not been accessed before, FREEVAR will go down by 1. (A dimensionless variable and an array with the same name are considered different variables, and string variables are considered different from numerical variables.) When FREEVAR reaches 0 and a new variable name is referenced, the system makes an "Out of memory" error.