@astro_addict Alternatively use Astrometry. Based on that you will see what is the delta to nominal FL in mm. Now you will have to adjust this by changing the distance between primary and secondary mirror. This is done by screwing central screw on the secondary mirror.
@Butzzze What you are seeing is probably related to stiction. In my case meshing of the geers was soo tight that belt was streathing too much while trying to correct the Dec backlash.
@Butzzze I would suggest that you loosen the Dec gear meshing. Also try the unidirectional Dec guiding. This is the approach that helped a lot in my case with cem26.