What about unstable line voltage? Do you have equipment kicking on and off on the same circuit as the enlarger, such as AC? This would create problems with color printing, but I think a voltage fluctuation would be in the range of 5-10%. I don't know if that's enough to cause a 20% exposure error. I'm guessing.
Paul
__________________
"Pictures are not incidental frills to a text; they are essences of our distinctive way of knowing." S. J. Gould
|