BTW, my method fits just about any reciprocity curve, but my observation that the correction for any film is a factor of tm^1.62 is limited to those films that believe in it. The factor happens to be the amount of correction required at 1 second of metered time. Any time anyone gets some additional experimental data, my equation and its assumptions can be tested. For instance, if you find that a particular film needs 200 seconds when the metered exposure is 100, the amount of correction is 100, and that is Af*(100^1.62), so Af*1738 = 100 and Af = .056. After a few such results, you can average AF and see how that average fits the trials that went into calculating it.