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.
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Maybe you measured a clocks accuracy over a period of time, like a month. That way any losses would be easier to spot as they’d accumulate?
You need to define “accurate”
For the caveman, the sun rising and setting was accurate enough for their daily lives
For the roman senate the sundial and a hourglass was accurate enough to know how long to to debate.
For traders on the sailships a spring loaded pocket watch was accurate enough to know time.
For the factory worker a DC powered clock was enough to know when to take a lunchbreak.
A crystal oscillator clock for a computer to have everything in sync.
For a scientist an atomic clock is accurate enought to measure subatomic processes.
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Accuracy is relative
Pendulum length.
The time it takes for a pendulum to swing back and forth is dependent only upon the length of the pendulum – not the sweep from side to side. A big sweep takes the same amount of time as a small sweep using the same pendulum. So the time period is the same when the pendulum first starts as it is when the pendulum Nears the end.
If a clock’s mechanism is being driven by a pendulum then the resulting movement is extremely accurate and reproducible.
The first clocks were accurate per definition. Sundials tracked the Sun’s position in the sky, and the time they showed *was* the correct time (i.e. if it marked “noon”, it was noon), because that was the time. Keep in mind that the idea of having hours of the same length is more recent, the first divisions of the day were proportional to how much it took from sunrise to sunset, so in summer “hours” were longer than in winter.
You don’t think the sun and stars would have made a useful target? They’re LITERALLY how humans navigated for thousands of years.
The meridian is the imaginary north-south line in the sky dividing east and west. Local noon time was originally (before clocks) defined as the time that the sun crossed the meridian. This definition of a day is a very precise 24 hours, to a very small fraction of a second, no matter what season.
They usually isn’t a need for an accurate time since time is a construct before clocks there were candles with nails meeting times set based on the sun a town bell and days were literally counted when clocks started replacing sundials there were big clocks usually near town squares like Big Ben that gave ppl an “accurate” or at least synchronized time to work with time isn’t inherently useful when it’s completely accurate but rather when it’s relatively the same or simpatico for many ppl
Our ability to judge the accuracy of time grew as ” clock technology ” grew.
At first, it was just the sundial. With a nice one, you can get within 5 minuets of the time of day. While we were in the sundial period, time was always relative to the sun. We didn’t really take into account ( or even know? ) that the day was just a little less that 24 hours.
Also, the sun and stars are pretty accurate. You can check this yourself if you want to. Find a longish tube, some cardboard, and something to hold the tube. Stick the cardboard on one end of the tube. You’re just using it to create shadow. point the tube at the sun so that you can see the full circle. Clamp it in place and start your clock.
come back the next day, 5 mins before the time that set the pole and see if you can see a difference. If you can, congrats, you just measured 24 hours to within 5 mins.
After that, we have the pendulum clock. here is where we can get pretty accurate.
The other thing that I haven’t seen mentioned (at least not explicitly) is that the development of modern, accurate every day clocks was a gradual process. It wasn’t a situation where someone said “here’s this thing I just invented called a clock that will perpetually keep the correct time.”
Prior to accurate time keeping methods, time was an estimate. Simple time keeping tools like sundials can get you in the rough ballpark. Early mechanical clocks had to be frequently reset to stay on time (I think typically adjusted at noon based on the sun). Over time, they developed new mechanisms until they got more accurate.
The one of the first “clocks” were sun dials, so they were directly using the sun to measure the passage of time
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