On the Gregorian revision of the Julian calendar (Q1100449)

The author points to the fact that the tropical year of \(365^ d5^ h49^ m16^ s=365.25^ d-1/134^ d\), found in the Alfonsine Tables, played a key role for the Gregorian calendar rule of reckoning 97 leap years in the four centuries whence in an average Gregorian year equals \(365.25^ d-1/133.\bar 3^ d\). Then he criticizes a succession of authors from L. Euler to N. Swerdlov for their attempts to explain the fraction 97/400 without reference to the Alfonsine year. Actually the tropical year decreases slowly from say \(365.2425^ d\) in the 3rd century B.C. to \(365.2422^ d\) in the 19th century. So it is not very interesting to learn that the Alfonsine year, set up in the 13th century and based on comparison with records from still earlier centuries, ``errs in excess by 30 seconds per year'' - although this is true on comparison with the 19th century value.