help to resolve IF statement that calculates 2 sums to zero with certain variables in calc

I am using the following [=IF(AA12=1,IF(X12<>0,X12-40,X12),IF(AA12=0.5,IF(X12<>0,X12-29,X12)))] calculation for a plus or minus calculation on a schedule which is based on 29 or 40 hours per week.
The problem is when scheduled hours = 29 or 40 hours I get a funky result calculation in the cell =IF(AA12>=1,IF(X12<>0,X12-40,X12),IF(AA12=0.5,IF(X12< -7.10543E-15
>0,X12-29,X12)))
I have not been able to figure this out
Anyone have any solutions???

The 1 = a true statement if full time and the .5 is if it is a part time 29 hours from a check box another sheet.

The original cell just above calculates perfectly. the cells below give a funky cell result.