system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did the people who made the first clock know what time it was?
gpt
Solar time is the oldest form of time measurement. This means that the length of hours varies depending on the season, along with the length of daylight.

Consistent units were developed based on calculations of the average length of daylight. With permanently running clocks, they could be accurately set by referencing solar time on a particular day of the year, or with sufficient knowledge you can adjust from current solar time by calculating the deviation from the mean on today's date. This is why accurate timekeeping was often the business of astronomical observatories.

It's actually a very recent phenomenon that we don't have to consult the sun to determine the time.