So I set up the tripod and 3-way tripod head, both of which are rated more than enough to hold the camera. I leveled the tripod and head using my trusty spirit level I keep in the camera bag. I then attached the camera to the tripod head and and re-leveled the tripod, placing the spirit level on the block under the bellows. I put the ground glass on and ensured all adjustments are neutral (no tilts, swings or shifts). However, the building directly in front of me does not line up with the etchings on the ground glass: one of the walls starts 1-2mm on the left of one line and ends up 1mm to the right of the line but if I adjust the tripod, I can straighten it all out where the wall runs parallel to the line (I think I can assume the etched lines are straight as it is a professionally made ground glass). However, the spirit level under the block now reads a non-level with a tilt to one side.

Which reading do I take as accurate? My initial reaction was if the camera is leveled properly, then use that. However, I also considered that what-you-see-is-what-you-get and if the building is not straight on the ground glass, why would it be straight on the film? Is it possible my adjustments were not truly neutral which caused the problem?

Thanks in advance.