HP Forums

It looks like the custom/user regression just plots the equation supplied by the user, but doesn't allow for fitting the parameter of a custom equation to data. Is that correct?

Also, at least for linear fit, is it possible to force the y-intercept to zero (i.e. Y=aX)?

Yes that is correct.
The custom fit is only for visual verification of known curves.
I thought that I could enter some expression and have a fitting done with that but was told that this is not intended. Maybe it is a feature that can be used in class - I did never use custom since then. I see no practical usage for it.