I have one of the very early MO in its production run. When the watch was new, it was gaining almost 20 sec/day - not exactly impressive at all. After a few rounds of rotation (got worn about a week every 3 months), it has settled down to about +15/day.
Perhaps I was bored, but I opened it one day to see what the movement is capable of. I had hoped to calibrate it to within the COSC spec.
After about 10 calibrations in 7 days, I arrived at the current calibration. Result - it is pretty much dead on every day (consistently from day to day), over a period of six days, it lost a total of .5 seconds.
Well, I have to say it has to be the most accurate watch in my collection right now. It is not only accurate, but the rate consistence from day to day is absolutely outstanding!
The finer point, turning the screw clockwise slows down the watch, counterclockwise speeds it up. It is very sensitive, it will gain 2-5 seconds for every quarter turn of the screw, so you have to be patient. And accuracy in a stationary position is also a little different from when the watch is being worn. I use a Witschi Expert II for baseline static timing, and then close it up and wear it for 12-24 hours for on the wrist timing.
And of course, do it in a dust free environment to keep the inside dust free.
I don't expect Stowa to be able to spend this much time (plus the new watches aren't run in yet) on the calibration. But if you have the right tool and the patience, you can get one heck of an accurate watch out of the MO. Just thought I would share it with you tinkerers out there.