Quoted from Damien:Any thoughts?
Calibrate it on a flat LEVEL surface!
You showed pictures of your readings with the level on the playfield. Show corresponding readings with the level on the floor between the front legs for reference. What we should find here is that your floor is not level in the direction front of machine to back of machine, as indicated by you seemed to get a decent pitch reading on the playfield with both the front and back levelers at their shortest setting.