Gregorian calendar has 365.2425 days per year

[barrycarter]

In our current Gregorian calendar, there are 365.2425 days, not 365.25. You should either correct for this or at least mention in the code you are using a non-Greogrian calendar.

[a-p-jo]

Thank you very much for opening this issue!

Yeah, the code says a year is 31557600 seconds, which is 365.25 days and is the unit used in the Julian calendar rather than the Gregorian one. This needs fixing; I hadn't quite realized this before.

On further research, I also discovered solar time and the concept of the mean tropical year.

Would you prefer the tool to use the Gregorian calendar year (365.2425 days) or the mean tropical year (365.24219 days)?

[a-p-jo]

@barrycarter In the latest commits, I've added the ability to select among half a dozen year types and the default is the gregorian year. This can be configured in config.h.

Let me know if this fixes the issue.

[barrycarter]

Looks great, thanks!