They had nothing to compare the clocks against, and I don’t think the stars and the sun would have made an useful target for comparison.
In: 17
All you had to do was measure when it was local Noon, i.e. when the Sun was at the Southernmost position.
You could either measure it with a compass or with a gnomon. The gnomon is basically a pole that projects a shadow. Keep marking where the shadow moves during the day, and the apex of the parabolic curve that you have drawn shows your local Noon.
Once that you have your local noon, you can set your clock and measure by how much it deviates until the following Noon.
You can find-tune the clock until it keeps time reliably between two noons.
Kind of a side story. But I recommend you read Longitude by Dava Sobel. It covers the invention of a seaworthy watch to help sailors with their Longitude by ensuring the watch remains accurate.
Short book overall, but it definitely piqued my interest. Great read for sure.
Oh I see the question…
I think the problem started when long distance electronic communication became a thing
Before that, having the seconds exact was not really needed
With internet, it was necessary to sync different device at long distance down to the second
https://endruntechnologies.com/time-sync-history
The stars are still used as a comparison target. They were the primary time reference up until the 1950s or 1960s.
Any given star will pass through the meridian of any location 366.2422 times per year, at an extraordinary degree of consistency. A star is directly overhead at midnight last night? It will be overhead at 11:56:04.091 pm tonight. A different star will be directly overhead at midnight. Given a catalog of star locations (which predate clocks by over a millennium), accurate sky observation tools (ditto), and a calendar (ditto again), and you can tell the time with very good precision (on clear cloudless nights).
In the 20th century we finally made clocks that were more consistent than the rotation of the Earth, and we stopped using the stars as the primary source of time.
The Sun is not as good for the most accurate timekeeping. The time between solar noon one day and solar noon the next varies by several minutes over the course of a year, and is only 24 hours on average.
If a stick is mounted perfectly perpendicular to the average surface of the Earth, it will cast a shadow that will make an arc, and you can mark out when the sun is just high enough to start casting a shadow, and also just before its so late its about to turn dark with no shadow. Somewhere near the middle, the shadow of the stick will be as short as it will be in a day, and that is when it’s as high in the sky as possible.
The taller you make the “stick”, the more accurate you can make the “sundial”. An obelisk is a tall pointy stick made of stone, and they were popular in ancient Egypt. The Washington monument is an Obelisk.
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQt07yUDK8oH0mluUE5R_aACf3k6X1nmbHbqg&usqp=CAU
There were ways such as comparing the shadows at Noon, but it’s also important to state that schedules were only ever as precise as the time keeping devices at the time.
Before clocks, the best someone could tell you was “be here mid-day tomorrow,” or something similar. Being 20 minutes late wasn’t really a thing since people couldn’t measure time that accurately. Once we got clocks, suddenly we could start scheduling things a little more tightly. The big “Town Clock,” on city hall or whatever was a good way for a town to all sync their clocks and watches together, but might be off compared to a neighboring town so nobody would ever expect someone to arrive after a 3 day journey precisely at 1:45.
As telegraph, radio, satellites, and digital communications became available, it allowed clocks from wider and wider areas to be synced, hence we gained the ability to keep (and expect others to keep) tighter and tighter schedules.
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