: Consulting my sources I have indicated that the Julian
: calendar had 365.25 days and I entered that into the
: equation: this may be wrong, patently wrong, as the new or
: modern calendar was created and necessarily updated to
: include the 1/4 day per annum, [...]

No, you were right. The Julian calendar had a leap year every four years, for an average year length of 365.25 days.

The current Gregorian calendar modifies that slightly: years that are divisible by 100 (century years) are not leap years, unless they are divisible by 400. (The current year 2000 is divisible by 400 and hence is a leap year, but the years 1700, 1800, and 1900 were not leap years on the Gregorian calendar). The Gregorian calendar therefore has an average year length of 365.2425 days, which is much closer to the actual astronomical value of 365.2422 days than is the Julian 365.25 day year. The average Gregorian year exceeds the true astronomical year by about 26 seconds.

We could come even closer by adopting a system of having 31 leap years every 128 years, that is, by having leap year every 4 years, except in years divisible by 128. This would give an average year length of 365.2421875 days, differing from the true astronomical year by only about one second.