I need help setting up an equation to take all the guess work out of designing a particular part.

I am designing a template that can be used by graphic artists to accurately place their artwork for a "slot machine". The part is a reel strip (or reel tape) which is secured around a mechanical reel (cylinder). The reel strip has a thickness that can vary from strip to strip depending on artist design and the effects that are applied. Think of it like a paper towel on its cardboard roll. The thickness drives the equations relating to circumference and arc length, but there are also two configuration possibilities for that particular thickness that drive the total length and overlap of the reel strip - either 11 or 22 (symbols). So for a given thickness we can have two possibilities:

A 11 symbol configuration which has a specific overall length (longer than the 22 symbol reel strip)

Or a

22 symbol configuration which is shorter than the overall length of an 11 symbol reel strip

I can set the thickness up as a Global Variable and the other equations are easy. But how do I set up equations and/or configurations to prompt the user for a choice of either 11 or 22 to drive the rest of the equations....or is that even possible? Or any suggestions?