I have a

CodePudding user response：

I solved this by modifying the formulas on this page. Changing the layout of the bands was a good first move.

Now, column I calculates the value from the current running total (matched from type in column A) and subtracts the value calculated in the same way but using the previous running total to give the amount applicable to the newly entered value on the same row in column H. I've some more testing to do but fairly sure it works correctly. Any other ideas, feel free to suggest!

Provisionally working sheet here: https://docs.google.com/spreadsheets/d/1e2pdyOi7dz_ZA8zfNtsHxieEUb5fiZGpD_FwRvkHyYw/edit?usp=sharing