Mathias: Thanks for the information about the compass. Somehow I had missed that. However I have some second thoughts about the KG12 stick grip. One (set) of the pictures from the instrument panel indeed show a KG12 stick grip. However several drawings show the KG2 control stick. The prototype first flew in November 1932 and the first production aircraft were delivered in May 1938. I haven't been able to trace the first use of the KG12 stick, however as the Heinkel He100, the Ju87A and the first Bf109s were still using the KG2 I assume the KG12 stick grip was not introduced before 1937.
Therefore it seem logical to expect most He51s were equipped with the KG2 stick grip. These are of course all assumptions, but in my experience manuals aren't always the most reliable sources. I can give you several examples where pictures for the manual were taken from a prototype which was different from the actual production model. Although the pictures from the instrument panel are quite well known, I don't know from which manual they come from. When they were taken from a manual which was used on the "Jagdfliegerschüle" in the period 1940-1942, I think it is logical to expect a KG12 stick grip. However for the pre-1939 aircraft I have some doubts.
Cheers,
Huub