What I did was putting a 210 5.6 lens on a slideviewer with that white plastic where light comes through. Above it i made a holder from paper where i put my gossen f2 light meter in precisely above the center of the lens. With that i measured the light at 5.6 8 11 etc... The F2 goes until /10 of a stop.
Next i put the imagon, placed the paper holder above it and moved the diafragm until my meter gave the same value at 5.6 as the other lens. So that was 5.6 I marked it and worked the same at 8,11 etc...
For all lenses the diafragm has the same width at for example 5.6.
What I also did in the past was printing a paper with a black circle that has the width of the 5.6,8,11 etc.. opening. Next put it on the slideviewer, place the shutter without lens onto it and close the diafragm until it has the same opening as the black spot on the paper.
very interesting and practical
"There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).