Dan, Of course you are right about the aperture diameter, but the OP asked about aperture scales, not aperture diameters. You are also quite right about the difficulty in physically measuring delicate aperture diameters and optically measuring small entrance pupils. The entrance pupil of my Leitz Super-Angulon 21mm is 0.65mm at the smallest aperture, not easy to measure with the 1mm graduations on my transparent scale.
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