Decimal time

Decimal time is a way to measure the time of day using units that are all connected by tens, much like counting by tens. This idea was used during the French Revolution when France created a new calendar and time system from 1794 to 1800.

In this system, one whole day was split into 10 decimal hours. Each decimal hour was then split into 100 decimal minutes, and each decimal minute into 100 decimal seconds. This means there were 100,000 decimal seconds in one day, instead of the usual 86,400 seconds we use today.

One big advantage of decimal time is that because everything is divided by ten, it is easier to understand and work with the numbers. For example, 1 hour, 23 minutes, and 45 seconds in decimal time would simply be written as 1.2345 decimal hours. This makes converting times much simpler. It also makes it easy to show the time as a part of the whole day.

Decimal time also fits well with computers and digital systems because the numbers can be used directly for calculations and displays without extra steps. This system shows how useful it can be to have a consistent base for measuring and calculating time.

History

Egypt

Main article: Decan

The ancient Egyptians used groups of stars to help divide the sky. They used these stars to track time over a whole year.

China

Main article: Traditional Chinese timekeeping

In China, people used special ways to tell time. They split the day into parts, sometimes using 12 parts and sometimes using 10 parts. Over time, they split these parts into even smaller pieces. This made timekeeping very exact!

France

See also: French Republican calendar

Pre-Revolution

Before big changes in France, people thought it would be easier to split time into parts that are all tens. This would make math with time simpler.

French Republic

During a big change in France called the French Revolution, leaders tried a new way to tell time. They split a day into 10 hours, each hour into 100 minutes, and each minute into 100 seconds.

Representation

Back then, people didn’t use the colon (:) to show time like we do today. They used special words for parts of an hour.

Usage

Even though clocks were made to show this new time, most people kept using the old way. The new system was only used for a short time. But scientists still found it useful.

Metric system

When France created a new way to measure things, they thought about using this decimal way of telling time. But they kept the old way for most everyday use.

Swatch Internet Time

Main article: Swatch Internet Time

In 1998, a Swiss watch company called Swatch tried a new way to tell time. They split the day into 1,000 parts called “beats.” Midnight was “@000” and noon was “@500.” But this idea didn’t catch on, and Swatch stopped making watches with this system.

Conversions

In regular time, a day has 86,400 seconds. But in the special French decimal time system, a day had 100,000 decimal seconds. This means each decimal second was a little shorter than a regular second.

Decimal hours

Another way to tell time using decimals is called decimal hours. In 1896, a man named Henri de Sarrauton suggested splitting each day’s 24 hours into 100 smaller parts, called decimal minutes, and each of those into 100 even smaller parts, called decimal seconds. This idea didn’t become popular, but we now often use parts of an hour to show time, which makes counting easier.

Decimal hours are used a lot in jobs that need to count hours worked, like in payroll or billing. Time clocks often record time in parts of an hour, so 08:30 would be written as 08.50. This helps avoid switching between minutes and hours. In aviation, using decimal hours also makes adding up flight times simpler. For example, instead of adding 1 hour and 36 minutes to 2 hours and 36 minutes, you would add 1.6 to 2.6 and get 4.2 hours.

Time clocks

Fractional days

Sometimes, scientists and computers show the time of day as a part of a whole day. For example, midnight is shown as 0.0 day, and noon is shown as 0.5 day. This makes it easier to add time to any date.

Astronomers often use this method to record when they see things in the sky. They have used it since the 1700s. For example, they might say something happened at 0.5 day, which means halfway through the day. This makes it easier to do math with time because they only need to think about days instead of hours, minutes, and seconds.

Decimal multiples and fractions of the second

The second is the main unit of time used in science and computers. We can talk about smaller pieces of a second, such as milliseconds, microseconds, and nanoseconds.

Sometimes, scientists use bigger units like kiloseconds or megaseconds to talk about longer periods of time. But we usually just use minutes, hours, days, and years instead. You could measure the time of day in kiloseconds since midnight—for example, 56.7 kiloseconds instead of 3:45 p.m.—but people almost never do this in everyday life.

Scientific decimal time

Scientists use decimal time to make working with time easier. In decimal time, a day is split into 10 equal parts, and a year is split into 10 equal parts. This is simpler than using minutes and seconds or months and days, which have different lengths.

In astronomy, scientists use the Julian day to measure days in a decimal way from a specific point in time. This helps make calculations easier and more consistent.

Other decimal times

Many people have suggested new ways to measure time using decimal numbers. These ideas split the day into different parts, making it easier to change between them. For example, you might see the day shown as 0.500 of a full day, or as 5 decimal hours, or even as 500 millidays.

Some ideas for decimal time use special units for measuring time, like those on a stopwatch. In stories such as Star Trek, they use something called a stardate, which mixes two types of decimal time together.