days-between-dates Solver equation for 17b

[Albert Chan]

(10-08-2018 09:44 AM)StephenG1CMZ Wrote:  I had been told that the reason December was called Dec although it was the 12th month now was because Julius added a month, and then Augustus copied him and added another month - not that it was because years used to start in March.
If both are true, December should be called October.

Based on https://stevemorse.org/juliancalendar/julian.htm

There were indeed a time with ten months per year. (Romulus calendar, 753 BC)
Later, Ianuarius, Februarius, Intercalarius (leap year month) were added (Numa calendar, 713 BC)

Originally, the months added were after December, until around 450 BC.
Numa calendar were shifted, with December as last month, just like today.