I finally got settled back in a bit from a month out of pocket and looked up the results from some analysis of the Kodak Development Dial that I did in late May and early June. At this point though, I'd pursue Gainer's model combining contrast index, time, and temp for individual film/developer combinations as a more successful and specific method.
This mathematical model for the Kodak Darkroom Dataguide Development Dial (discontinued some years ago in favor of tabular data) doesn't account for varying films and developers as has been discussed previously in this thread, and it's a generic formula derived from one part of a somewhat generic tool.
To adjust development time for a change in temperature using degrees Farenheit in a way that conforms closely to the Kodak Development Dial:
New Time = Old Time * exp(-0.0469*(New Temp - Old Temp))
Worst case from Dial #30 through Dial #50 and temperatures between 60F and 80F gets you within +/-4% of matching the results from the dial, much of which is probably noise from Kodak's rounding to 1/4 minute intervals, especially at shorter development times.
The use of this particular formula is not original with me. It can be found at
http://covingtoninnovations.com/xtol/index.html (with a very slightly different coefficient) and elsewhere. I don't know the original source for correct attribution. Note that Covington says it works with "most" developers, not all.
BTW, this derivation from the Kodak Development Dial would replicate the error noted in the case of DK-50 as per Gainer's recent comments in this thread, and is subject to the same criticisms that PE made earlier in this thread about ignoring the individual non-linear adjustments made using the several adjunct steps involved in using the Development Dial properly.
Lee
Linear Mode
