8 ms·

Decimal Time: How the French Made a 10-Hour Day (2013)

39 points by dirktheman 7y ago

jlarsen 7y ago
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.
- taejo 7y ago
  > it really isn't simpler with 10 and 100. Only if you ignore the complexity of teaching a whole population to do arithmetic in a different base.
  - jlarsen 7y ago
    Not what I said. I said that, sub-dividing days is not really simpler with base 10, and that sub-dividing time is pretty important practical aspect of time-keeping.
    - taejo 7y ago
      Repeating the same thing you said before isn't the best way of clarifying what you mean, but fair enough, I do now understand what you're trying to say.
- dirktheman 7y ago
  Do we really divide units of time that often, though? Only 'half an hour' and the quarters (in French at least) are used frequently. And with the decimal time system, 'quarter of an hour' would be just as meaningful as the Gregorian system, it would just signify 75 minutes instead of 45. Keep in mind they introduced the entire metric system: distance, volume, weight, currency, etcetera, making this just one of many changes... Either way, apparently people weren't too stoked about having one day off every 10 days instead of one day off every 7 days.
  - jlarsen 7y ago
    I do. I sleep 8 hours, wake up 2 hours before work, work 8 hours, and spend 6 hours in the evening afterwards. That's 1/3, 1/12, 1/3, and 1/4 of the day, or 3.33, 0.83, 3.33, 2.5 decimal hours. You have a good point about taking it in context with the 'decimalization' of other units of measure, but my point is really just that the article is overly generous towards decimal time, and ignores solid mathematical reasons for using 12/24/60 for time-keeping. I've never in my life needed to know when a day is "70% over", but I constantly need to subdivide my time into halves, thirds, or quarters.
    - masklinn 7y ago
      > I do. I sleep 8 hours, wake up 2 hours before work, work 8 hours, and spend 6 hours in the evening afterwards. That's 1/3, 1/12, 1/3, and 1/4 of the day You do realise that you use these approximations because they're the integral results of easy calculations, and you'd just use slightly different durations in a decimal time framework, right? As in, metric countries don't use a 12.7mm wrench because that's what 1/2" is. They use a 13mm wrench (and the corresponding metric nuts). And their speed limits are 110/120/130, not 112.6/120.7/128.7.
      - lifthrasiir 7y ago
        But we still have preferred numbers [1] which never map neatly to the decimal or any other radixes due to their logarithmic nature. The ratios, sharing the same logarithmic nature, ARE one of the good reasons to select radixes if the decimal were not as pervasive as now. [1] https://en.wikipedia.org/wiki/Preferred_number https://en.wikipedia.org/wiki/Preferred_number
- garmaine 7y ago
  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 7y ago
    If binary has taught me anything, is that you can count up to 1024 with 10 fingers...
    - masklinn 7y ago
      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)
    - Anarch157a 7y ago
      Using your hands to signal 4 in binary could put you in a lot of trouble.
  - rakoo 7y ago
    Not a single person I've met has ever used knuckles as a way to count anything, especially time.
    - garmaine 7y ago
      You obviously haven’t lived in ancient Babylonia. (Pro tip: different cultures have done things differently across time and space!)
- cm2187 7y ago
  I am not so sure of that. People are pretty comfortable using decimals for distances in the metric system. And you can always switch to the unit below. [edit] In fact the reason we don't use decimals for time is probably precisely because it is not using a metric system. What does 1.3h means? 1h and 18 minutes or 1h and 30 minutes?
  - granshaw 7y ago
    That’s the same problem inches and feet suffer from now and it’s horrible
- ginko 7y ago
  This seems about as convincing as the arguments that inches and feet are somehow more intuitive.
- swebs 7y ago
  By that logic, you must really love the imperial measurement system.
- mysterydip 7y ago
  Part of me wishes the majority were born with 12 digits on our hands instead of 10, so base 12 would've been the norm and everything would have the divisibility benefits mentioned
  - 116 7y ago
    Good thing you have 12 phalanxes and a thumb to point at them. That way you can count to 12. It's uncommon but doable.
  - Anarch157a 7y ago
    You can do base6 (which is almost as good) with your fingers. Use one hand for units, the other for tens, this way, you can count to 50b6, which is 35 in base10.
- BlueTemplar 7y ago
  Sadly, the dozenal system was basically done for after the release of "The Art of Tenths" by Simon Stevin in 1585, and the resulting adoption by traders and tradespeople. But well, the decimal system is probably the second best... My main gripe these days is the lack of consistency : while hours/minutes/seconds are not too bad, having computer screens in inches annoys me a lot ! (While TV screens are in centimeters, as expected.)
  - mrguyorama 7y ago
    >While TV screens are in centimeters, as expected. This is not my experience in America. We have both computer monitors and TV screens in diagonal inches
    - BlueTemplar 7y ago
      I know - guess whose fault is it that those measurements in diagonal inches are still around ?
vinc 7y ago
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 7y ago
  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.
  - vinc 7y ago
    Indeed, using the day as the fundamental unit may be a nice choice for humans on this planet as a personal system, it's equivalent to looking up and telling the time by the position of the sun in the sky, but it's not accurate nor regular due to celestial mechanics, so the second used by the metric system is much more universal and unlikely to change anytime soon. Thanks to our computers that keep track of every seconds elapsed since Unix Epoch, I can use them when I want to convert from my personal system to any other system or vice versa: $ geodate 51.1789 -1.8262 $(date +%s --date "12:00 +0100") --format "%c:%b" 45:33 hours:seconds => timestamp => centidays:dimidays
iraldir 7y ago
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 7y ago
  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!
toastal 7y ago
Time to start counting in seximal https://youtu.be/qID2B4MK7Y0 https://youtu.be/qID2B4MK7Y0
UncleSlacky 7y ago
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#Current_date_and_time> https://en.wikipedia.org/wiki/French_Republican_calendar#Cur...
- ddebernardy 7y ago
  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 7y ago
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.

39 points by dirktheman 7y ago

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.

taejo 7y ago
> it really isn't simpler with 10 and 100. Only if you ignore the complexity of teaching a whole population to do arithmetic in a different base.
- jlarsen 7y ago
  Not what I said. I said that, sub-dividing days is not really simpler with base 10, and that sub-dividing time is pretty important practical aspect of time-keeping.
  - taejo 7y ago
    Repeating the same thing you said before isn't the best way of clarifying what you mean, but fair enough, I do now understand what you're trying to say.
dirktheman 7y ago
Do we really divide units of time that often, though? Only 'half an hour' and the quarters (in French at least) are used frequently. And with the decimal time system, 'quarter of an hour' would be just as meaningful as the Gregorian system, it would just signify 75 minutes instead of 45. Keep in mind they introduced the entire metric system: distance, volume, weight, currency, etcetera, making this just one of many changes... Either way, apparently people weren't too stoked about having one day off every 10 days instead of one day off every 7 days.
- jlarsen 7y ago
  I do. I sleep 8 hours, wake up 2 hours before work, work 8 hours, and spend 6 hours in the evening afterwards. That's 1/3, 1/12, 1/3, and 1/4 of the day, or 3.33, 0.83, 3.33, 2.5 decimal hours. You have a good point about taking it in context with the 'decimalization' of other units of measure, but my point is really just that the article is overly generous towards decimal time, and ignores solid mathematical reasons for using 12/24/60 for time-keeping. I've never in my life needed to know when a day is "70% over", but I constantly need to subdivide my time into halves, thirds, or quarters.
  - masklinn 7y ago
    > I do. I sleep 8 hours, wake up 2 hours before work, work 8 hours, and spend 6 hours in the evening afterwards. That's 1/3, 1/12, 1/3, and 1/4 of the day You do realise that you use these approximations because they're the integral results of easy calculations, and you'd just use slightly different durations in a decimal time framework, right? As in, metric countries don't use a 12.7mm wrench because that's what 1/2" is. They use a 13mm wrench (and the corresponding metric nuts). And their speed limits are 110/120/130, not 112.6/120.7/128.7.
    - lifthrasiir 7y ago
      But we still have preferred numbers [1] which never map neatly to the decimal or any other radixes due to their logarithmic nature. The ratios, sharing the same logarithmic nature, ARE one of the good reasons to select radixes if the decimal were not as pervasive as now. [1] https://en.wikipedia.org/wiki/Preferred_number https://en.wikipedia.org/wiki/Preferred_number
garmaine 7y ago
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 7y ago
  If binary has taught me anything, is that you can count up to 1024 with 10 fingers...
  - masklinn 7y ago
    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)
  - Anarch157a 7y ago
    Using your hands to signal 4 in binary could put you in a lot of trouble.
- rakoo 7y ago
  Not a single person I've met has ever used knuckles as a way to count anything, especially time.
  - garmaine 7y ago
    You obviously haven’t lived in ancient Babylonia. (Pro tip: different cultures have done things differently across time and space!)
cm2187 7y ago
I am not so sure of that. People are pretty comfortable using decimals for distances in the metric system. And you can always switch to the unit below. [edit] In fact the reason we don't use decimals for time is probably precisely because it is not using a metric system. What does 1.3h means? 1h and 18 minutes or 1h and 30 minutes?
- granshaw 7y ago
  That’s the same problem inches and feet suffer from now and it’s horrible
ginko 7y ago
This seems about as convincing as the arguments that inches and feet are somehow more intuitive.
swebs 7y ago
By that logic, you must really love the imperial measurement system.
mysterydip 7y ago
Part of me wishes the majority were born with 12 digits on our hands instead of 10, so base 12 would've been the norm and everything would have the divisibility benefits mentioned
- 116 7y ago
  Good thing you have 12 phalanxes and a thumb to point at them. That way you can count to 12. It's uncommon but doable.
- Anarch157a 7y ago
  You can do base6 (which is almost as good) with your fingers. Use one hand for units, the other for tens, this way, you can count to 50b6, which is 35 in base10.
BlueTemplar 7y ago
Sadly, the dozenal system was basically done for after the release of "The Art of Tenths" by Simon Stevin in 1585, and the resulting adoption by traders and tradespeople. But well, the decimal system is probably the second best... My main gripe these days is the lack of consistency : while hours/minutes/seconds are not too bad, having computer screens in inches annoys me a lot ! (While TV screens are in centimeters, as expected.)
- mrguyorama 7y ago
  >While TV screens are in centimeters, as expected. This is not my experience in America. We have both computer monitors and TV screens in diagonal inches
  - BlueTemplar 7y ago
    I know - guess whose fault is it that those measurements in diagonal inches are still around ?

vinc 7y ago

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 7y ago
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.
- vinc 7y ago
  Indeed, using the day as the fundamental unit may be a nice choice for humans on this planet as a personal system, it's equivalent to looking up and telling the time by the position of the sun in the sky, but it's not accurate nor regular due to celestial mechanics, so the second used by the metric system is much more universal and unlikely to change anytime soon. Thanks to our computers that keep track of every seconds elapsed since Unix Epoch, I can use them when I want to convert from my personal system to any other system or vice versa: $ geodate 51.1789 -1.8262 $(date +%s --date "12:00 +0100") --format "%c:%b" 45:33 hours:seconds => timestamp => centidays:dimidays

iraldir 7y ago

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 7y ago
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!

toastal 7y ago

Time to start counting in seximal https://youtu.be/qID2B4MK7Y0 https://youtu.be/qID2B4MK7Y0

UncleSlacky 7y ago

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#Current_date_and_time> https://en.wikipedia.org/wiki/French_Republican_calendar#Cur...

ddebernardy 7y ago
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 7y ago

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.