Denotation of values don't allow whitespace and other signs

I am allowed to insert whitespaces in the table of increments, but if I'm using this variables in the formula, it's just writing "error" after the equation.

Because I like my long and whitespaced names, i'd like to add whitespaced variablenames... maybe we can internaly replace the whitespaces by _?

For short way: disallow white spaces in increments... as well as signs like / or + and so on...