The parameter editor dialog box is klunky, and could do with some improvements. From simple to complex:
1. When expression goes red, give an explanation as to what the problem is. For e.g. its non-obvious when entering atan(x) that the problem is a units mismatch, and not say a misspelling of the function name. Perhaps at least make the units go red is that's the problem.
2. Auto set the units from the result of the expression. E.g. set to degrees in above case.
3. Offer auto complete drop down for reserved words (like for other parameter names). Perhaps also show parameter names expected for that/those function(s).
4. Add a help button to display a list of in built in functions.
5. Slightly off topic, but also (as suggested previously) make parameters available in sheet metal rules settings.
