will you please try to uncheck (in the calculation dialog) the option "Do not evaluate if all referenced fields are empty". You can also try to "store" the calculation result - if you get a warning, maybe that'll lead somewhere.
Are you using a Calculation Field or a Numeric field with calculation? You should have a Calculation field
Assuming this calculation is in the Invoice table? If so, then you should know that calculation updates do not trigger when related data change. So if the value in Qualification::Additional Unit 01 changes, the calculation in Invoice won't be updated.
To trigger it to change, you need local data, like this:
Let ( [
trigger = ModificationTimestamp ;
If ( IsEmpty ( Qualification::Additional Unit 01 ) ; "" ; 6 )
where ModificationTimestamp is a timestamp field that auto-enters the modification timestamp. If you have another local field (in the same table) that you would like to use as a trigger, that would be fine, too (dependent on business rules).
Thanks all for your quick and helpful replies. It was a simple fix; I had not set the field to Calculation, it was just Number. As a dunce at FMP it appears illogical that I need to, but there we go. Thanks again.