When
you define two or more calculations in a form, the order in which
they are carried out is the order in which you defined the calculations.
In some cases, you may need to modify the calculation order to obtain
correct results.

For example, if you wanted to use the result
obtained from calculating two form fields to calculate the value
of a third form field, the first two form fields must be calculated
together first to obtain the correct final results.

Acrobat automatically performs all assigned field calculations
when you are creating and testing your form fields. For convenience
while you work, you can turn off automatic calculation in the forms
preferences.