The program has a number of in-built numeric variables which can be used to store the results of operations or in programs.

These are:-

a, b, c, d, l, m, x, y Simple numeric variables.
pp[ ] An array variable which can have subscript values from zero, (pp[0]), up to the current number of columns, (pp[number of columns]).
st[row:column] This is not strictly a variable but acts as one for the purposes of storing data and displays. It references an element of the stored data by row and column. e.g. st[3:2] refers to the third number in column 2.

In the last two cases it is essential to use square brackets, [ ], rather than round ones.

The program also allows you to use pi, (p), and e