I need a script that looks at a field and calculates a tolerance then looks at a separate text field and makes sure it is within that tolerance and places pass or fail in a separate text field

Calculation scripts can be tricky because they are executed anytime any field on the PDF is changed. So extra care has to be taken to ensure calculations are done in the proper order and that scripts don’t interfere with one another.  

The behavior you’ve described could indicate out of order calculations. Try checking the calculation order.