
Decimal Time: How the French Made a 10-Hour Day (2013) - dirktheman
http://mentalfloss.com/article/32127/decimal-time-how-french-made-10-hour-day
======
jlarsen
Fun little snippet of history =), but something that seems to get missed often
in time-keeping is that 12, 24, and 60 are not accidental, they're used for a
good reason - they're highly divisible numbers.

12 is divisible by 2, 3, 4, 6

24 is divisible by 2, 3, 4, 6, 8, 12

60 is divisible by 2, 3, 4, 5, 6, 10, 12, 15, 20, 30

Compare that to

10 (divisible by 2, 5) and

100 (divisible by 2, 4, 5, 10, 20, 25, 50),

and you start to see the problem. You can't split a 10 hour day into quarters
without a decimal, and you can't split a 10 hour day into thirds without an
infinite decimal or a fraction.

"

But in 1793, the French smashed the old clock in favor of French Revolutionary
Time: a 10-hour day, with 100 minutes per hour, and 100 seconds per minute.
This thoroughly modern system had a few practical benefits, chief among them
being a simplified way to do time-related math...

"

isn't really true. Sub-dividing days and hours into smaller, equal pieces is a
critical part of time-keeping, and it really isn't simpler with 10 and 100.

~~~
garmaine
Actually the reason we have base-60 time is that we have 5 fingers on one
hand, and 12 knuckles that can be pointed to by the thumb on the other.
5x12=60.

Of course why the Babylonians went with this two-mechanism system instead of
doing the same thing on both hands is probably because of divisibility. Get a
prime factor of 5 from one hand, and prime factors of 2 and 3 from the other.

(Also note that you can count 12 hours on one hand, a full 24 on both.)

EDIT: AFAIK the Babylonians didn't have a developed number theory, and I'm not
sure they even had a formal idea of prime numbers. But we do know from
surviving accounting "textbooks" (practice tablets & instructions) that both
they and the near-contemporary ancient Egyptians understood the special
divisibility of these numbers.

~~~
jarfil
If binary has taught me anything, is that you can count up to 1024 with 10
fingers...

~~~
masklinn
If you've got flexible hands and independent-enough fingers you can even count
in ternary, up to 59048 (though binary can also take advantage of toes for a
limit of 1048573)

------
vinc
There's a clock using French Revolutionary Time exposed at Musée des Arts et
Métiers if you happen to be in Paris and want to see one.

I've been using centidays (and dimidays) for a few years now and it works well
for me as a personal time keeping system in combination with local time (at
local noon the sun is at its highest point in the sky and the clock shows
50:00) and a lunisolar calendar. More on that here:
[https://geodate.org](https://geodate.org)

A centiday is precisely 864 seconds, and 4 centidays is almost equivalent to 1
hour (3456 seconds) so it's not too hard to make rough conversions.

I made a little Fitbit app so my watch could display the time (with the
longitude given by the GPS of my phone) and I have a sundial in the garden
that works just as well. It's quite fun to play with time keeping systems.

~~~
phicoh
In the context of the metric system, the problem is that the second and the
'day' don't line up. From a human time keeping point of view, days and
fractions of days would be ideal.

However, actual days are nowhere close to a fixed amount of time. And for
historical reasons we are stuck with a very precisely defined second that is
based on 24 hours in a day.

So the obvious approach would be to define a new unit of time that is roughly
equivalent to a milli- or microday.

But the chance of that happening is close to zero.

So we are stuck with the second as the fundamental unit of time. Having a
'centiday' as 864 seconds would be even more removed from the principles of
the metric system than a 3600 second hour.

~~~
WorldMaker
Sci-fi writers, most notably Vernor Vinge, have played with Metric Time [1] of
the modern sort of being entirely second-based.

It's interesting because it particularly exposes interesting flaws in using
metric prefixes (that are sometimes also talked about in the world of grams
where kilograms are the closer unit to most "human applicability" and that a
more human scale would possibly have more prefixes near kilogram than gram).
Particularly the magnitude jump from a kilosecond (16.7 minutes, about a
quarter hour) to megasecond (11.6 days, nearly a fortnight).

I've heard fun proposals that if Metric Time based on seconds were to be more
useful on human timescales to bring back the deceased Metric prefix myria-
[2]. A myriasecond is 167 minutes or just less than three hours (2.78). Maybe
a prefix for the next digit as well (10^5) which would be just more than a
day, by about an eighth of a day (27.8 hours).

[1]
[https://en.wikipedia.org/wiki/Metric_time](https://en.wikipedia.org/wiki/Metric_time)

[2]
[https://en.wikipedia.org/wiki/Myria-](https://en.wikipedia.org/wiki/Myria-)

~~~
phicoh
It is mainly what we are used to. For power we have kilowatt, megawatt,
gigawatt, no problem. For gram, meter and second, we have milli, micro, nano,
etc. no problem.

But we don't have megagram, megameter because we not used to it.

Just like you can easily talk about 10 km, 20 km, etc. you could easily talk
about 10 ks, 20 ks, etc. no need for a special name. We are just not used to
it.

~~~
WorldMaker
It's not just about what we are used to. The argument about where the
"central" point in the scale matters (for seconds and for grams) because the
prefixes are by their very nature logarithmic, with "easier" distinctions made
close to the center point/0-point on the scale axis than further away in the
scale.

milli-, centi-, deci-, deca-, hecto-, kilo- are all six very close surrounding
the 0-point/origin. Everything else gets logarithmically further out.

Using second as the 0-point is great for computation, as milliseconds and even
microseconds can matter to a computer, but it isn't great for the human
perception of time where people are bad at even granulizing events that happen
in deciseconds, leaving nearly all of the decimal prefixes almost useless in
human timescales.

Which is why you see the French Decimal Time system mentioned in the article
here and used by the poster above in this thread centered around the day as
its 0-point. milliday, centiday, deciday, decaday, hectoday, and even kiloday
are all relatively useful units in a human timescale.

While you are correct that we don't "need" that kind of vocabulary, the
argument is that it would be _useful_ in conversation and in day-to-day (fig.
and lit.) math. Having additional prefixes serves as mental anchors/frames for
the conversation. If I give a number of seconds to you as hundreds of
milliseconds versus deciseconds, that gives you additional context about my
methodology and/or focus in whatever that benchmark was. Sure, you can easily
convert between the two prefixes, but that context can be _useful_.

Just as the difference between if I tell you something is happening in
hundreds of minutes from now versus threes of hours from now. There's probably
a useful contextual distinction there. That's why people play with solutions
like Decimal Time changing the scale altogether away from seconds to something
more like an Earth day, or in the other direction explore ideas with more
prefixes to fill in some of the logarithmic "gaps" such as myria- and hebdo-.

~~~
phicoh
I'd say that for time, the second is the only thing people can really relate
to. With a bit of practice everybody can count seconds. We cannot related to
minutes, hours, day, etc. without an external time keeping source.

The other thing worth point out is that, though we have centi-, deci-, deca-,
and hecto- they get only limited use in practice.

Very few distances are specified in deca- or hectometers.

Very few things are decagrams. There is a metric ounce and pound. But
hectogram is not used.

So for distance, we have meter, kilometer. For mass, gram, kilogram, metric
tonne.

Within the same system, we could easily deal with kiloseconds and megaseconds.

As far as I know, nobdy uses deciseconds as something other than a weird way
of saying 100 milliseconds.

In informal speech, the number of zeros is used as estimate of precision.
Using prefixes to specify precision is way too confusing.

Within the metric system, 10 kilosecond would roughly be the same as 3 hours.
With a single day, everybody could easily adapt to kiloseconds. The problem
starts when you have to create a system of timekeeping based on metric second.

~~~
WorldMaker
> I'd say that for time, the second is the only thing people can really relate
> to. With a bit of practice everybody can count seconds.

Not really. Games like "one Mississippi" are fun approximations, but they
aren't terribly accurate. Also this gets very close to the argument that foot
is a better unit for length than meter because you can more easily approximate
it with the average adult male's shoe length. Easy to approximate has its
uses, but also doesn't necessarily make it the best fit for every application.

Scheduling is a critical component to people needing time, and yes is just
about impossible without clocks / calendars / sundials / other "external
sources". But that's also where all the interesting stuff happens when people
use time and if you can't account for the math of scheduling, people would
never use that unit for time.

Part of the problem there is that we do keep trying to "square the circle" if
we want to apply metric tendencies to our reference points on rotating
spheroids. (Another fun experiment I've seen in sci-fi, and played with
myself, is the idea of day time expressed in radians.)

------
iraldir
The mention at the end of "Internet time" made memories long forgotten rush
back to my mind. A friend of mine had a watch like that. Did I too? Not sure.
But it was the coolest shit ever, that's for certain.

~~~
twic
Swatch Internet Time!

[https://en.wikipedia.org/wiki/Swatch_Internet_Time](https://en.wikipedia.org/wiki/Swatch_Internet_Time)

Usually, when there are posts about decimal timekeeping on HN, it falls to me
to remind everyone about Swatch Internet Time, so i'm overjoyed that this
time, you've brought it up!

------
UncleSlacky
If you want to know the current(ish) decimal time (and date according to the
French revolutionary calendar) it's kept updated at Wikipedia:
<[https://en.wikipedia.org/wiki/French_Republican_calendar#Cur...](https://en.wikipedia.org/wiki/French_Republican_calendar#Current_date_and_time>)

~~~
ddebernardy
It's unfortunate that the script doesn't output whatever is associated with
the current day. The revolutionaries had at the same time replaced name days
with something else to celebrate each day. They were agricultural in nature
(crops, animals, etc.), with a tool thrown in every 10 days. Which must have
felt like a giant FU to peasants when you think of it: Your day off will now
be every 10 days instead of 7 - and you'll be celebrating e.g. the plow during
that day.

------
a_random_name
When I worked for the post office, our pay keeping clocks were 24 hours to a
day with 100 minutes to the hour. It was super weird to look at a clock and
see that the time was 18:79. Eventually I got used to keeping time in quarter
hour increments, because the math lined up well enough.

------
toastal
Time to start counting in seximal
[https://youtu.be/qID2B4MK7Y0](https://youtu.be/qID2B4MK7Y0)

