88 lines
3.9 KiB
Markdown
88 lines
3.9 KiB
Markdown
template: post
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title: Time rant
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author: flewkey
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timestamp: 1620014860
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license: CC-BY
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Bob wants to talk to a group of people who live in different areas. What time
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standard should Bob use to schedule the call? How about
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[Coordinated Universal Time](https://en.wikipedia.org/wiki/Coordinated_Universal_Time)
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(UTC)? It is the internationally agreed upon standard for world time, so Bob
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should be able to use it, right?
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Unfortunately, life is not so simple. If Bob scheduled a call for “05:00 UTC”,
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one other person will show up on-time. The rest will try to join at 17:00
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(05:00 p.m.) in whatever their local time zone is. Frustrating situations like
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these are responsible for
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[countdown timers](https://www.timeanddate.com/countdown/create)
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becoming so common nowadays.
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This insanity has been driving people mad since the beginning of time, but
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this is not the fault of individual people who don’t understand what “UTC” is.
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This is a systemic issue which ought to be corrected. If everybody learns to
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read analog clocks in primary school, they should learn about time zones as
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well.
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---
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### 12-hour time and 24-hour time
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In 12-hour time, the clock wraps around every 12 hours, dividing the day into
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two periods: “a.m.” and “p.m.”. This is terrible, as it creates ambiguity
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when most people and clocks tell the time. The number “12” is also used in
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place of the number “0” for some reason, going against how numbers usually
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wrap around. Seeing 12-hour time on a digital clock makes me feel nauseous.
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In 24-hour time, the clock wraps around every 24 hours, once per day. That’s all
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there is to it.
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#### To convert 12-hour time to 24-hour time:
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1. Add 12 hours if it is “p.m.”
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2. If the hours column is equal to 24, set it back to 0
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#### To convert 24-hour time to 12-hour time:
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1. Subtract 12 hours if it is 13:00 or greater
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2. If the hours column is equal to 0, set it to 12
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---
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### Time zones 101
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A time zone is just an area that follows a time standard. However, if computers
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all synced to different time standards depending on the region, that would be
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terrible. Instead, most of them sync to Coordinated Universal Time (UTC)
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instead. Then, they apply a positive or negative offset to UTC before formatting
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the time and displaying it to users.
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As far as most people should be concerned, offsets are just acronyms that
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represent offsets from UTC. For example, [Central European Time](https://www.timeanddate.com/time/zones/cet)
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(CET) is one hour ahead of UTC. This means that it is also represented as
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UTC+1 or UTC+0100. Some time zones need more than an hour of precision as well.
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For example, [Newfoundland Standard Time](https://www.timeanddate.com/time/zones/nst)
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(NST) is represented as UTC-3:30 or UTC-0330.
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Look up your time zone on [this map](https://www.timeanddate.com/time/map/).
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Memorize the acronym and UTC offset. Also understand that it will roll forward
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by an hour when [Daylight Saving Time](https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst)
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(summer time in Europe) applies. This will allow you to understand UTC time in
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relation to your time zone.
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If you can remember the acronyms for other time zones, you will also be able to
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convert between them in your head. This is a useful ability to have.
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Some common time zones in North America worth remembering are
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[Eastern Standard Time](https://www.timeanddate.com/time/zones/est) (UTC-5),
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[Central Standard Time](https://www.timeanddate.com/time/zones/cst) (UTC-6) and
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[Pacific Standard Time](https://www.timeanddate.com/time/zones/pst) (UTC-8).
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---
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### Conclusion
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Those who made it to the end of this post can count themselves among the few
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capable of reading time properly. If you thought time zones were interesting,
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wait until you hear about timekeeping. The NIST has a
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[great page](https://www.nist.gov/pml/time-and-frequency-division/time-services/utcnist-time-scale/how-utcnist-works)
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describing how time standards are kept. The rabbit hole goes deep.
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