Thanks great feedback and completely agree about the clunkiness around sums!

As a mitigation I did add row highlighting (if you hover over a var it'll highlight the row it was defined at), but the underlying problem of dynamic sums is still there.

I was working on a TOTAL() function (which someone also mentioned in this thread), but conceptually I also think some of the calcs are better in a tabular format, so have been toying around with designs with tables etc.