Which is why I suggested
- Delete custom fields Width, height and days
- Only use custom field “H * W * days”
- User only types into custom field “H * W * days”
- Copy and paste from custom field “H * W * days” into “Qty” field
I appreciate that is not the solution you want but entering calculation has been an Idea for several years so this is the best you can to at the moment. see Customizable Calculation Report - #5 by Patch