These data sheets put those numbers out with an air of certainty, and they very well may be spot on, but. . .if your metering is not absolutely perfect, those numbers are less than meaningless.
Take the measured time and multiply it by 7.5 then
raise this product to the power 1.42 then
divide the result by 10.
This should be very close to the correct exposure time.
If tonal matching over a range of reciprocity influenced exposures is required then development compensation is called for.
I don't compensate development because I like the reciprocity induced contrast increase (John Sexton's "Quiet Light" theory) for dimly lit landscapes.
__________________ Photography, the word itself, invented and defined by its author Sir John.F.W.Herschel, 14 March 1839 at the Royal Society, Somerset House, London. Quote "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..". unquote.
The r-square for the above function is 1.0, indicating a perfect fit over the range of data used. Technically, plugging in calculated exposures of greater than 100 seconds is very risky. Within the range 1 to 100 seconds, this function should work very well if Kodak supplied the right data!
The data in the current Kodak tech info for TXP, and the formula derived from it by Dr. Louie are both essentially perfect matches for a data sheet and generic Kodak B&W film reciprocity information dated in the mid 1970's. While TXP is an older style film, I believe it's been updated, as have all other Kodak films since that time, most of them with changed reciprocity characteristics requiring less compensation. My personal take, based on a bit of my own shooting and on reading the results of testing by others, is that Kodak hasn't really tested reciprocity carefully and published updated information for all their emulsions, and that TXP is likely to fall into that group of films.
I'd test for any critical applications. If it's not critical, the Kodak suggestions are OK for a reasonable estimate, but you might find yourself a stop or more off the mark.
Reciprocity is a funny bear, and personal taste in density and contrast isn't considered in the published charts. I use the published data as a way to judge the general failure rate of the film, then test. I don't think there is a single film I've shot to failure that has given me the results I sought at the published compensations. YMMV.
Reciprocity Formula - Tri-X 320 
Linear Mode
