Bad arithmetic conversion

Synopsis
An error in some mathematical expression/assignment, for example attempting to add a numeric value to a variable whose value is not numeric, as so:

my_var = "hello"
sum = my_var + 30
Cause
You stored a numeric value in a variable, and then when using that variable, you put the name of the variable in quotes, thus mistakenly using the variable's name rather than its numeric.

Cure
Do not put your variable name in quotes when used in a mathematical expression.

Cause
You used a variable that was never assigned any value. Therefore, its default value is its name in capital letters. A variable's name is not a numeric value.

Cure
Make sure that you assign a numeric value to the variable before using it in some mathematical expression. You can trap the NOVALUE condition to catch errors of this nature.