Use one field to calculate another and vice-versa?

[scrambledmeggs]

We're using a base to track actual work done on multi-project invoices, but the invoices from different vendors format the info differently - some tell us a percentage of the time worked spent on each project, while others tell us $ amount subtotals by project. I have a table recording the actuals from each invoice, which includes a "Project Percent" field and a "Project amount" field, and I can enter the info on each invoice in either field and leave the other blank, but is there any way to have the populated field do the math against the invoice total to automatically fill in the other field that's left blank? I can't see any way around the problem that having the fields update one another reflexively would cause a circular logic error. Anyone have any ideas on how I can automate filling in percentage when I have $ amount, and fill in $ amount when I have percentage? 

[TheTimeSavingCo · Accepted solution]

Hmm, you'd need to have a third formula field that'll calculate the value for you.  So if "Project Percent" is filled and "Project Amount" is empty, it'll generate the "Project Amount" value. 

Then, you'd have an automation that would trigger whenever this third field was not empty, and it would have a conditional action to update the appropriate field with the value in the third field based on which one was empty, does that make sense?