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