When a form's final amount appears one edit behind, first document the arithmetic relationship you expect. A small calculation tree is easier to examine than a realistic invoice containing discounts, tax rules and dozens of input fields.

Use an Acrobat desktop practice form containing Quantity, Price, Line and Total. Work with fictional numbers and retain a copy of the existing field definitions before changing their order.

Put the dependency first

Acrobat calculates fields in an order that matters when one result feeds another. For Line = Quantity × Price and Total = Line + 5, Line must precede Total. With Quantity 2 and Price 7, expect 14 and 19; changing Quantity to 3 should produce 21 and 26.

In All tools > Prepare a form, inspect each calculated field's Properties > Calculate settings. Confirm that the definitions express those relationships. In the Fields pane's Options menu, choose Set field calculation order. Move Line before Total using Up or Down, then confirm.

Commit the quantity edit by leaving the field and inspect both results. A final total that becomes correct only after another unrelated edit has not passed this exercise. Repeat from 3 back to 2 as well as from 2 to 3.

Keep arithmetic and presentation separate

Write the four expected results in the test notes before performing the exercise. If the subtotal itself is wrong, investigate that relationship before attributing everything to the final field's order. Record the first incorrect result rather than only the last number on the page.

Use the intended recipient's viewer for a separate acceptance check before distributing an operational form. Record that viewer and version with the outcome; a successful exercise in your authoring environment is evidence about that environment.

Keep the calculation definitions, their order and the two input scenarios together. The useful handover is a reproducible dependency check, not a screenshot of one coincidentally correct total.

Sources: Adobe: calculation order.