Orca Docs: https://github.com/SoftFever/OrcaSlicer/wiki/tolerance-calib
BambuLabs Wiki: https://wiki.bambulab.com/en/software/bambu-studio/xy-hole-contour-compensation
https://www.obico.io/blog/tolerance-test-in-orcaslicer-a-comprehensive-guide/
From: u/hotellonely on Reddit is this great concise explanation:
[Imagine] in your model, you have 2x holes with 1mm diameter, and their distance between their centroid should be 10mm. You also have a corresponding part that can be clipped into the holes.
Shrinkage: After you print, you found that the distance of centroids is 9.97mm. translating to a 99.7% shrinkage rate.
XY Hole: After you print, you found that the diameter the holes is 0.9mm. You apply a 0.05mm compensation to fix it back to 1mm. (XY comp work in radius, so you apply 0.05 to get 0.1mm extra diameter)
XY Contour: After you print, you found that the corresponding part cannot fit into the holes because it's too large, like 1.1mm diameter. You can apply a -0.05mm Contour compensation to fix that.
Or if it's too loose, apply a 0.05mm contour compensation to fix that.
Basically correct Shrinkage is the base of everything, starting from there you can start to work with Hole and Contour compensations.