You didn’t become Facebook friends 46 years ago. So, where does the number come from. It isn’t random. It is a result of how time is calculated in computing. Unix Time is how most programmers calculate and store time. It is the number of seconds (not counting leap seconds) since the Unix epoch, January 1, 1970, 00:00:00 UTC. Unix time is incredibly useful on the Internet because it allows you to store time independent from timezones. (If you are not sure why timezones strike fear into the hearts of programmers, watch Tom Scott explain why on Computerphile.)

So, say you want to see exactly how many years it has been since two people became friends on Facebook. Instead of trying to subtract dates like this...

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