Leistungsbuch?

[Peter]

I came across a Leistungsbuch and I have never seen one before, didn’t even know that such books existed. Wherpass and Flugbuch I know about but can someone help me out of the function of the Leistungsbuch? I can see that it has been filled in with the same pencil covering quite a period in time, several years so it doesn’t looks like it has been updated daily. Was it the owner who filled it in for his own sake? Did it have any formal function? Was it populated with mission information? Any information is much appreciated, also if it has a value.

Mary Christmas!
Peter