Quote Originally Posted by Bruce (Camclicker)
This is a simple formula I've been working with to reduce temp of stock to by adding cold water to make a working solution to be used immedieatly.


X=((A/B)-(C/(B-D)))*-(B-D)

A = DESIRED FINAL TEMP -- F
B = TOTAL # PARTS OF BOTH SOLUTIONS
C = EXISTING STOCK TEMPERATURE -- F
D = # PARTS OF DILUTION WATER ONLY
X = NEEDED TEMPERATURE OF DILUTING WATER ONLY

To make an 8 oz 68 degree solution from 72 degree stock solution at 1 + 2 ratio would be:

55=((A[68]/B[8])-(C[72]/(B[8]-D[6])))*-(B[8]-D[6])

This works for me when tempering small amounts for processing rolls of 35mm. It may not be sophisticated, or beautifully written, but it works.
You forgot to factor in windage.