Originally Posted by DREW WILEY
Peak 1 in conjunction with an enlarger will measure smaller distances than a consumer grade caliper.
In terms of focusing on the paper or the baseboard, I don't have an opinion on the matter, just the optical formula that predicts about a 2mm focus spread at f2.8 at 9x enlargement. This easily encompasses any photographic paper or film of which I am aware.
Modular transfer function focusing equation (equation #38 in http://www.largeformatphotography.in...DoFinDepth.pdf) :
N_max ~ 20 / (1 + m) sqrt(dv)
N-max = F number
m = magnification
dv = focusing leeway on the baseboard
20 = constant for circle of confusion about 0.15mm on the print