Inspired by distance scale issue, I measured all lenses in hand, combine same focal length lenses into one, and plotted the curves representing them.
Most lenses marked as same focal length have same characteristic curve, except 120mm lenses I have.
One is Schneider Angulon 6.8/120mm, and another one is a vintage Tessar 4.5/12cm lens from Cocarette folder. Their characteristic curves are totally different, funny thing isn't it? That means two 120mm lenses need different distance scale.