Calculate the sum of all the values of a question within a roster and use it as a validation condition

I am working with a hh level questionnaire and I am struggling in setting the validation condition for a question within a roster.
The question is “What share of %crop% was dedicated to %a specific use% during %refperiod%?”. I want to make sure that the share of crop dedicated to different uses sum up to 100 maximum.
The question that starts this roster is a multiselect question with the list of possible crop uses. Then, the question regarding the share of crop dedicated to each selected use is within the roster.
In other words, if the respondent says that he uses potatoes for home consumption, selling and animal feed, I want to make sure that when specifying the shares of potatoes corresponding to each activity, their sum does not exceed 100.
Thank you in advance for your support!

Hello @MartinaF ,

just use the Sum() function.

See the “Burgers” section in the “Public example User
questions and common patterns” questionnaire for an example of use.

Please make sure you have undergone some training regarding the Survey Solutions questionnaire design.

Best, Sergiy

Dear @sergiy,
Sorry but I cannot find the example that you have indicated, can you send me the link?