After careful study I decided to touch and adjust only the Digitizer Horizontal Gain, step H11, R42 on board A9 (very difficult to reach the trimpot, augh!).
Now the horizontal scale is in agreement with the real signal scale, and the two waveforms (real and digitized) superimposes almost perfectly.
So I prefer do not touch all other various calibration points, since the digitized waveforms shows no gross and obvious aberrations.
The 7854 is a splendid scope but calibrating it gives me a headache!