Applying logic in calculation rule fast formula for Competencies Section (Performance Documents)

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Applying logic in calculation rule fast formula for Competencies Section (Performance Documents)

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Would it be possible to apply some sort of logic in the Fast Formula? For our competencies section, we have a set of competencies. Some are appropriate for the employee, some are not. Manager will evaluate all the appropriate ones and leave the optional (not appropriate) ones blank. We would like to exclude the value of the unrated ones.

The current behavior is whenever the manager skips them for rating, they are still being included in the calculation and their equivalent value is 0.

If possible, may we get a reference please? Or some suggestions would really help. Thank you very much!