# Why doesn't p.m. start with 1 o'clock?
**URL:** https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580
**Category:** Factual Questions
**Created:** [February 19, 2009, 6:51pm UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580 "2009-02-19T18:51:10Z")
**Posts on this page:** 5
**Page:** 2
### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [February 20, 2009, 12:59am UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580/21 "2009-02-20T00:59:55Z")
> [@beowulff](#):
>
> Then, I suggest you start a movement to change the way clocks are labeled. You can team up with Dvorak and the Metric crowd.
>
> Maybe [Timecube](http://www.timecube.com/) would be interested.
The French Revolutionaries already tried it:
> **[Decimal time](https://en.wikipedia.org/wiki/Decimal_time)**
>
> Decimal time is the representation of the time of day using units which are decimally related. This term is often used specifically to refer to the French Republican calendar time system used from 1794 to 1800, during the French Revolution, which divided the day into 10 decimal hours, each decimal hour into 100 decimal minutes and each decimal minute into 100 decimal seconds (100,000 decimal seconds per day), as opposed to the more familiar standard time, which divides the day into 24 hours, each...
And look where THAT movement wound up … at least the Swatch folks didn’t start beheading people …
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [February 20, 2009, 1:26am UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580/22 "2009-02-20T01:26:15Z")
> [@Vox\_Imperatoris](#):
>
> Yes, but it’s only 365.25 days because of the arbitrary length of the second, minute, and hour (mainly the second, since it’s just a completely arbitrary length of time that was settled on long ago, although I realize that they have precise SI ways of defining what that arbitrary length is). And I was just making the point that the rest of the time measurement system is completely arbitrary, even where it does make sense to some degree, so there’s no reason to expect the placement of the noon hour to coincide with what makes the most sense in the OP’s mind.
>
> Valete,
> Vox Imperatoris
Uhhhh… No. It’s 365.25 DAYS. Nothing to do with seconds, minutes, or hours.
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### Author:  [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)
#### Post date: [February 20, 2009, 1:28am UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580/23 "2009-02-20T01:28:46Z")
Yeah. Sure, a lot of it is arbitrary, and your overall point still stands, **Vox** , but a year being around 365.25 days is entirely non-arbitrary; as **beowulff** said, the amount of time it takes for the Earth to complete a full motion around the sun is about 365.25 times the amount of time it takes for the Earth to complete a full turn around its axis. That’s not a number that someone made up; that’s a measurement that was made of external physical quantities.
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### Author:  [@Vox\_Imperatoris](https://boards.straightdope.com/u/Vox_Imperatoris)
#### Post date: [February 20, 2009, 1:30am UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580/24 "2009-02-20T01:30:58Z")
> [@beowulff](#):
>
> Uhhhh… No. It’s 365.25 DAYS. Nothing to do with seconds, minutes, or hours.
You’re right. :smack: Besides the naturally-occurring relation between the length of time it takes for the Earth to spin around on its axis and the length of time it takes to revolve around the sun, the rest of it is arbitrary, though.
Valete,
Vox Imperatoris
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### Author:  [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)
#### Post date: [February 20, 2009, 3:03am UTC](https://boards.straightdope.com/t/why-doesnt-p-m-start-with-1-oclock/486580/25 "2009-02-20T03:03:56Z")
> [@CC](#):
>
> I don’t think that’s the question. I think it should be as I framed it - why doesn’t noon happen at 1 o’clock, when the change in numbering happens? When we go from one day to the next, the numbering system should coincide, and we should go from counting in the 12’s to counting in the 1’s. When the new day starts, the numbering system should start over.
It does, it starts at 0. 12:00 noon is the END of the twelfth hour, not the start of it.
Think about it this way. When we ask “what time is it?” what do we want to know? IMO we want to know how much time has elapsed in the day. The current system tells us how much time has elapsed, your system wouldn’t. If it’s 1:30am then one hour and thirty minutes have passed since the start of the day. And if it’s 1:30pm, one hour and thirty minutes have passed since noon. That makes a lot of sense to me. On the other hand, if we started at 1pm being noon, then when it is 2:30 it tells us that one and a half hours have passed since noon, but we have to do some (simple) math to arrive at that answer. Far far easier to start our numbering at zero as we do.
Likewise with someone’s age. Using your system a baby would be “one” upon vaginal exit. When they’d spent two and a half years since birth they’d be “three and a half”. That is not useful in any way, and neither is starting the day at 1:00am.
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