[df cardwell]

From a table by J.M. Eder,
published many times,
taken here from “Developing”,
by CI Jacobson,
13th edition, Focal Press, 1955.

“The increase in speed of develpoment with an increase of 10˚ Centigrade is taken as the Temperature Coefficient of the developer. For example, if we find that a certain developer works twice as quickly (at 25˚ as it did at 15˚), then we say it has a Temperature Coefficient of 2."

While I think this is only useful as a guide, it IS helpful to see the factors in play.

Temperature Coefficients of Various Developers
Metol-Soda 1.5
Metol-HQ 1.7-1.9
HQ-Soda 2.2-2.6
Pyro-Soda 2.2-2.4
Rodinal 2.0
Glycin-Potash 2.5-2.7
Pyrocatechin-Potash 2.8

This should illustrate why a single correction curve for all developers is invalid. FURTHER, films play a factor. In Kodak published curves,
you can see that D-76 and Microdol-X are sometimes, but not always, parallel.

While a single correction factor is a good estimator,
so is an experienced hunch. A notebook usually is much better .

Rodinal, whose times should double from 59 to 77 degrees F, comes close with some films, but depending upon the degree of development (gamma, or CI). Here are three AGFA curves, for 3 well-missed films. See that the the lines curve, and are seldom parallel. Two Rodinal dilutions are shown, as well as Studional/Rodinal Special.