Hi,
At my organization, we ask a lot of constant sum questions, but we also want to let our respondents skip them when they don't have the relevant data. As of now, it seems impossible to allow respondents to skip questions when 'Must Total' is selected. I think it would be ideal if the 'Must Total' validation was "activated" AFTER respondents enter ANY data into one of the constant sum boxes. So, in effect, if respondents don't enter any data, they can skip it without triggering the validation rules.
The folks over at Product Ideas suggested I post the question here. Does anyone have the custom code to make this work? Thank you in advance - I'm a newbie with javascript!
Also, I have added this request/idea to the Product Ideas page, and I've asked if they can allow the validation to be changed to 'Request Response' at a minimum or, ideally, if they can "activate" the validation as described above.
If you think this should become a standard feature, please upvote it here: https://community.qualtrics.com/XMcommunity/discussion/16460/request-response-not-force-for-constant-sum-questions/p1?new=1 . 
Thanks,
Dr. Josh Kahn