Autocomplete Rule for Restricting Manager from Capturing Specific Rating in Overall Section

Summary:

Based on the "Manager Calculated Rating" in Overall Summary section, we want the Managers to be able to choose the "Manager Rating" in the Overall Summary section same as the value in "Manager Calculated Rating" or one level up or one level down and no other values. How can we achieve this?

Content (required):

Suppose, the Manager Calculated Rating as shown in Overall Summary section is 3.4 based on individual goal rating multiplied by the goal weightage and the sum of them, the Calculated Rating is considered to be mapped as 3. Now, we must put a restriction as such so that the Manager can capture the "Manager Rating" Overall Summary as either 3 or 2 (and not below 2) or 4 (and not above 4).