Precession--Jumping from 1875 to 1950 I'm looking at a book that was written in 1967. The only star catalog available for the author's purposes was from 1875. He needed to have the precession for 1955 data. In his program code, he makes a call to precco(0.75) to update the coefficients of the precession routine, preces. preces is called twice right after that to two vectors. Each vector is replaced by a new vector with precession applied. I'm fairly sure that this is to jump 75 years (expressed as 0.75) and somehow move from 1875 to 1950. I do not see any code that gets the precession updated to 1955. Close enough at 1950, I guess?? Comments? Does this seem like a valid way to get to 1950?