Quote Originally Posted by Frank Szabo View Post
Couldn't reciprocity failure be expressed as one would a limit? (think beginnings of the calculus - not the stuff on one's teeth).
The important bit in this reciprocity failure thing is expressed by the word failure.
If there was an easy rule, an unequivocal relation, a simple formula, Bunsen and Roscoe would have found it ages ago.

You can explore the behaviour of films, and compile tables.

But - and this is important - you cannot (!) calculate reciprocity failure.