OK – Just a little update.
I’ve managed to tune the inclinometer to be spot on. I simply took a sheat of 800 grit dry/wet paper and grinded the sides of the inclinometers aluminium housing. Also put the inclinometer on a 100% level surface – and turned it around 180 deg. – and it is now spot on.
If you have the same problem with your inclinometer I’ll gladly explain more detailed exactly how to solve this issue!