How can we prevent calculated ratings until all the ratings are entered?

We are using calculated ratings for calculating overall ratings. We have a requirement that we need to prevent calculated rating from populating until Manager has provided all the ratings on the particular section, and prevent the overall performance rating from populating until all the section ratings have populated.

This need arose because of this scenario: When manager begins the evaluation, he provides some evaluation comments and saves the document for later. He has not yet provided any ratings to the goals, but overall goals rating shows as the lowest rating(the calculated rating). We are aware that when manager will provide all the goals ratings, the overall goal rating will re-calculate the correct one, but the managers being end-users panic seeing the lowest rating getting calculated initially.