[QUOTE=GrahamWelland;369634]...all seem to be different - that's on the tripod, the Cube, my Alpa STC and the IQ160.[QUOTE]
This is my finding as well and since I rely on spirit levels in my photography it became a pain. My solution was to spend the time necessary (1 hour +) to finetune the levels on the Alpa SWA. Now both horizontal and vertical are perfectly aligned with the sensor so I can confidently rely on them. In fact, the are so exact that it is only about 1-2 images in 10 that I rotate 0,5-1 degrees, the vast majority are completely straight and untouched in regards to rotation.
The time spent was well worth it and now I ignore all other spirit levels on tripods etc.