On Saturday, December 9, 2017 at 2:53:41 PM UTC, Mikko wrote:



The accuracy of the best clocks before pendulum clocks was abut 15
minutes per day. Before about 1650 the best pendulum clocks'
accuracy was about 10 seconds per day. In order to determine the
equation of time with a clock even one second per day, achieved by
Harrison in about 1760, is very little. Only in 1870 was accuracy of
0.1 seconds per day achieved, and equation of time determined with
a clock.

Mikko

The Equation of Time(keeping) determines 12 noon as a function of the 24 hour day when two shadows line up exactly as the Sun crosses a longitude meridian -

"Draw a Meridian line upon a floor and then hang two plummets, each by a small thread or wire, directly over the said Meridian, at the distance of some 2. feet or more one from the other, as the smallness of the thread will admit. When the middle of the Sun (the Eye being placed so, as to bring both the threads into one line) appears to be in the same line exactly you are then immediately to set the Watch, not precisely to the hour of 12. but by so much less, as is the Aequation of the day by the Table."

https://adcs.home.xs4all.nl/Huygens/06/kort-E.html

They later discovered an easier method and a shortcut to check the accuracy of a watch once they had the average 24 hour day by using two foreground references and the return of a star to the same position each 24 hour day. The Equation of Timekeeping refers the 24 hour day to the Latitude/Longitude system an therefore a rotational rate of 15 degrees per hour.

Assigning significance to circumpolar motion and using a watch is a different matter altogether and that is where everyone went astray. It takes people with a dual interest in astronomy and engineering to look at how the average 24 hour day substitutes for constant rotation at 15 degrees per hour insofar as the neat transformation of 'average' into 'constant' is at the heart of the Lat/Long system, planetary geometry and planetary rotation.