This document is part of the Martian Time Boneyard. It was originally located at http://www.marsengineering.com/Calendar/Clocks.asp.
Author: Shaun Moss

Clocks

Many different clocks have been proposed for use on Mars, yet we couldn't decide on one in particular that would satisfy all requirements. A system of units derived from the sol is necessary, as are access to Earth units such as the second. Our solution is to offer two clocks running synchronously, namely, the decimal and HMS (hours, minutes, seconds) clocks.

The Decimal Clock

Most members of our group preferred the modern decimal format. Decimal time systems have been proposed for Earth for many years (see http://www.decimaltime.org/). It's a very difficult thing to ask the people of Earth to switch to a decimal time format, because the 24 hour, sexagesimal clock is so ingrained. However, when colonizing Mars we have the opportunity to invent all manner of new and better systems.

Interestingly, the 24 hour system originally came from base 10 anyway. The ancient Egyptians, who always used base 10, even 10 day weeks, divided the daylight into 10 hours. Two more were added for twilight, and the night was also divided into 12 hours, the length of which varied according with the seasons. Greek astronomers adapted this system by dividing a day into 24 equal hours, each of which was subdivided into 60 parts using the sexagesimal system of the Babylonians.

Decimal clock designs have been around for a long time, but the names we adopted for units are those suggested by Bruce Mackenzie. Bruce proposed a decimal clock for Mars in which the sol was divided in the following way:

Dividing the sol into horas introduces the unnecessary complication of making the clock quadragesimal (base 40) rather than decimal. One of the main reasons for decimal time is that adding and subtracting times becomes much easier. Sexagesimal arithmetic is not easy, and errors can be easily made even when performing a seemingly simple task such as calculating a timesheet. Removing the hora results in a purely decimal clock with this arrangement:

The sol begins at 000.00 and ends at 999.99.

If people still require a unit of time equivalent to an hour, they can still use 40 mils. However, because the timeslip clock is running alongside, they can just switch modes and measure hours using it.