# Universal Decimal Time

## The Universal Decimal Time clock

### Graphical UDT clock

The UDT clock cannot be displayed because JavaScript and HTML5 Canvas support are both required.

### Text-only UDT clock

The text-only UDT clock cannot be displayed because JavaScript support needs to be enabled in your browser.

## What does the UDT clock mean?

It's very simple. The UDT clock shows the percentage of the day that has already passed, where zero is midnight by UTC (Coordinated Universal Time, which is centred on longitude zero on the globe). No matter where you are in the world, the Universal Decimal Time will be the same, as it is always zeroed on UTC and does not change with timezones and there is never a daylight saving adjustment.

When the time is 00:00 (midnight) on a UTC clock, the UDT clock will show 00%0000.

When the time is 12:00 (noon) on a UTC clock, the UDT clock will show 50%0000. That is, fifty percent of the UTC day has passed.

Just before midnight UTC, the UDT clock will show 99%9999. That is, ninety-nine point nine-nine-nine-nine percent of the UDT day has passed. Then it will tick over to 00%0000 at UTC midnight.

Because the UDT clock divides the day into tens (every digit on the clock can be a number between zero and nine), none of the digits on the UDT clock represent a value of exactly one second. In fact, the digits of the UDT clock have the following values:

First digit: units of one deciDay
Represents tenths of a day, and the time between ticks is 2.4 hours, equal to 144 minutes, equal to 8640 seconds.
Second digit: units of one centiDay
Represents hundredths of a day, and the time between ticks is 14.4 minutes, equal to 864 seconds.
Third digit: units of one milliDay
Represents thousandths of a day, and the time between ticks is 1.44 minutes, equal to 86.4 seconds.
Fourth digit: units of one-hundred microDays
Represents ten-thousandths of a day, and the time between ticks is 8.64 seconds, equal to 8640 milliseconds.
Fifth digit: units of ten microDays
Represents hundred-thousandths of a day, and the time between ticks is 0.864 seconds, equal to 864 milliseconds.
Sixth digit: units of one microDay
Represents millionths of a day, and the time between ticks is 0.0864 seconds, equal to 86.4 milliseconds.

## How does the UDT clock calculate the decimal time?

Again, it's very simple. (In fact, too simple.)

The UDT clock gets the time from your computer's internal clock, converts it to UTC and then calculates how many milliseconds have passed in this day so far (where zero is midnight UTC). It then performs the calculation:

(number of milliseconds passed) divided by (total number of milliseconds in one day)

and the result is a raw decimal value, for instance 0.5 at noon UTC, or 0.0 at midnight UTC. The raw decimal value is converted into a percentage (by multiplying by 100) to make it more understandable and then padded with trailing zeroes (if necessary) so that it is always six digits long. Then the decimal point is replaced with a percentage symbol so that the final result has the standard UDT form, for example 00%0000 at the start of a UTC day or 99%9999 at the very end of a UTC day.

This gives a very simple method for calculating Universal Decimal Time, but is flawed because not every day has the same number of seconds. In fact, once a year or so, a day may have one or two 'leap seconds' added to it to make sure that UTC is linked with the rotation of the Earth.

The UDT clock does not currently take into account these variations in day length. While this will only make a very slight difference to the value displayed, it does mean that the UDT clock is not suitable for very technical applications.

More likely to be a problem is the fact that the current UDT clock on this page relies on the time taken from the visitor's computer. So if the visitor's computer has the wrong time, or even the wrong time zone, the UDT value they see will be wrong. (A future version of the UDT clock might incorporate NTP to factor away time errors.)

## What's the purpose of the UDT clock?

No point really. Bob just wanted some practice in web development, and decided to make a clock that displayed the time in a standardised decimal form.

As UTC is often used to give the time of astronomical events, events that are of potential interest to anyone on the globe, possibly Universal Decimal Time could be used in a similar way to give the time of live events that are available globally, on the internet for instance. As the UDT clock shows a decimalised version of UTC, and only UTC, it does not vary its output from one timezone to another, so it could be used as a global clock for organising events such as live web broadcasts.

Of course, UTC could be used anyway, but this might lead to confusion. Seeing, for instance, 21:30 UTC might trick people into forgetting that the event time is in another timezone, and they may miss the event. Seeing 90%0000 UDT would make it very clear that the given time is not of a local timezone.

But this is all speculation. It is very unlikely that the UDT clock will be used for anything more than decoration on a small number of websites.

## Is this an original idea?

Certainly not. There are already many forms of decimal time. In fact, there are clocks that display the same decimalised UTC (or UT1 which is the astronomers' version), but in the raw decimal form rather than as a percentage. Even though the presentation might vary, the value displayed should be numerically the same on all such clocks.

There are also decimal clocks that do a similar thing, but are zeroed on a different place (that is, zeroed on a time which is not midnight UTC). This seems like a bad idea, because UTC is the scientific standard for worldwide time, and breaking standards leads to everlasting confusion. For instance, how do you interpret the following date: 01/02/03? A Scandinavian would read it as 2001 February 3rd. A Briton would read it as 1st February 2003. An American would read it as January 2nd 2003. Without agreeing on a standard, shared information often becomes effectively meaningless, so the UDT clock uses UTC as its time basis.

## Can I put the Universal Decimal Time clock on my web page?

Yes. See the page about how to show the UDT clock on your own web pages.