Converting a number to a percentage?

I work in beverage "manufacturing" and I'm using Acrobat 8.x  to create a form that the shift supervisors can complete at the end of each shift. In it, they're going to record their production numbers, and I'd like to have the form compare their output numbers with the "ideal" output numbers, and present the result as a percentage. I've been able to sort out everything, to determine their "pieces per shift", but when I try to have that cell's number divide against the cell that contains the "ideal pieces per shift", I get back an error stating "The value entered does not match the format of the field." That being said, I've determined this afternoon, that I am entirely too stupid to figure this out. I tried changing the format of the cell from Percentage to Number...but then it doesn't display the percentage(duh). I'm hoping that there is an easy solution.