Calculated Field - Count selections in related module

Hi all,

In our Tasks-module there's a custom dropdown field with a product selection. I would like to see what's the highest "product interest" per individual contact based on the number of tasks with the appropriate selections.

From my understanding I have to add a custom field in tasks for each selection that holds either 1 or 0 based on if that certain option is selected or not. let's call them trigger_p1, trigger_p2...

In the contacts module I would add another calculated field "counter". Here I would either add the values of each trigger field (or count those with value=1), then compare and set my desired value based on the comparison. Is this the right apporach? Seems like a lot of overhead if there are several options in the initial selection field...

PS: Unfortunately we're still running Sugar 7.9.5.0