The formula bar shows a formula, but a nested expression may still hide the reason for an unexpected answer. Formulas > Evaluate Formula lets you inspect the calculation as its references are replaced with their current values. Read each stage before moving to the next one.
Start on the cell you are investigating. The Evaluation box shows the current expression. Click Evaluate until you reach the final value. Restart returns to the original expression, so you can compare its references again.
This is especially useful for order of operations, logical tests and zero denominators. Show Formulas complements it by displaying formula text across the worksheet instead of results. Neither command repairs the model. After you locate the cause, edit the formula or the input cell that needs changing.