[MontyCarloHall]

They both fit Gaussians, just different ones! OLS fits a 1D Gaussian to the set of errors in the y coordinates only, whereas TLS (PCA) fits a 2D Gaussian to the set of all (x,y) pairs.

[ryang2718]

Well, that was a knowledge gap, thank you! I certainly need to review PCA but python makes it a bit too easy.