system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Was the time synchronized between continents (to the minute, with differing hours) before the Internet?
gpt
Synchronized time between continents dates back to the Age of Sail, where ships would carry clocks synchronized to a master clock at the Royal Observatory in Greenwich England.

They would then compare celestial observations such as the local time for sunrise & sunset to the time in Greenwich, to determine how far east or west from the Greenwich Meridian they had sailed.

(As an aside, you may be wondering how chronometers on ships can easily be synced to a clock at a land-based observatory? They'd have a ball on a pole on their roof, easily observable by telescope from ships, and would drop it at a pre-determined time each day. Much like what's going to happen in Times Square tomorrow night, although the original Time Balls usually signaled 1pm at the *start* of their drop, instead of Midnight when it hits bottom.)

However, individual locales would keep their own local times up until the Age of Railroads. The difficulty in keeping trains on time when every small town along the line had their own local Noon lead to a push to standardize time into the timezones we know today.