Using JavaScript with True/False Buttons

Phil is right, that Math has a more elegant solution (as we knew he would),  Still, philosophically, while both solve the problem of duplicating entries, I would favor Phil's answer because more of it can be done in SL. My rule of thumb about javascript is to use it only as a last resort, and as sparingly as possible. That is based solely on the thought that in the future, if this project needs to be modified or maintained, there may not be a programmer available.

Understand that this particular problem cannot be solved without some js, but my counsel is the less, the better.

My answer above steps you through the same solution that Phil is proposing.