There's one thing I can't quite wrap my head around while reading literature on the Tully-Fisher relation: why is the fitting always performed in the magnitude-log(velocity) space? It may be easier to fit an expression y = mx + b to data than y = c*x**z, but one would have to deal with asymmetric errors in two dimensions.

I'm currently trying to figure out a way to do the fit in semi-log space, namely, magnitude-velocity space, using errors in both directions and MCMC.

I'm currently trying to figure out a way to do the fit in semi-log space, namely, magnitude-velocity space, using errors in both directions and MCMC.