Adding a + or - tolerance on values in formulas

I was trying to create a formula for 4' and 8' track lights. The takeoff quantity was hit and miss for working with my formula because I was ending up with some 4.00' measurements that were actually 4.0001' or something and so my formula wasn't working right.

Could we get the ability to apply a + or - tolerance on formulas? I believe this would also be useful in other applications even in increments of 1" or 2" if desired.