FAQ: AZ Mount Pro
Second ... You must make sure your OTA is loaded with all the bits you are going to use and is BALANCED in both the DEC and AZ, this is important. Also, leave about 5mm of thread showing on the level adjusting screws to be able to make the adjustments needed.
To level...As you know the mount base is round and only a small diameter (150mm). The bubble level is placed on the outside edge of the mount and it rotates on bearings that are fitted in cast mouldings which may or may not be accurate but each mount will be different so what I’m going to describe will work on each and every mount regardless of how the bubble level has been fitted. To do this we need reference points and in the MT/PRO we have built-in ones i.e. the level-adjusting screws.
What you do is rotate the mount until the bubble is over one of these screws, wait for the bubble to settle then adjust the bubble until it is somewhere near the centre, take note of the position of the bubble and then rotate to the next reference point which is the next level adjusting screw, take note of where the bubble is and adjust it to half between the last one and this. Rotate to the next and last level adjusting the screw and do the same... Keep doing this until you get the bubble in the "SAME" position over all three reference points (level adjusting screws). It does "NOT" matter that the bubble is "NOT" in the centre, what matters "MOST" is that the bubble is in the "SAME" position over all three reference points then you will be level...
The final position of the bubble may be different from mount to mount (because of the way the unit has been fitted) but that does NOT matter because it will still be level.
(Credit to Graham Beazley)