Hi,
The propeller blade pitch indicator "clock" is a pure indication of propeller blade setting. The indication is presented exactly as a 12 hour clock face, with each 10 min division of the large hand equal to one degree of blade pitch and each "hour" equal to six degrees. The precise pitch of the blade position is slightly different to the indicated setting, because each different propeller type and engine could have a different basic setting, stated in the aircraft manual. This made the "12 O'clock" setting universally correct and was used for the Take-Off blade position, on all types.
The "clock" indication wound anti-clockwise as the blades were coarsened with increasing airspeed.
This function has often been incorrectly misreported as the "clock" winding clockwise with increasing pitch, famously written in error in the American Intelligence write-up of the German propeller system.
Today, these instruments are valuable on the collectors market, and several reproductions have been produced.
Eng