There are two functions, GetErrorYhigh() and GetErrorYlow, where the docs erroneously write "It returns the error along X at point i." - it must be Y.
I would fix it myself, but I don't have the recent root source.

Maybe it would be worth adding a word about "high" and "low" errors in the corresponding place. What "error high" or "error" would be if there is only "error" or "error high"?