Question

Is there a formula for the difference (delta) between two entries?

Answer 1

If you expect that someone takes the time to read your questions and understand your needs to help you the best way possible, you should at least take the same time to formulate a proper question that explains your needs.

Pasting the title twice and thats it, does not help explaining anything.

If you mean 3 - 6 = -3 or 6 - 3 = 3, just use simple math in the Notion formula.

prop("one") - prop("two")

Just remane one and two with your column names.