There are some points I would like to make:

First: I am glad people are taking the initiative to do something instead of just wringing their hands and lamenting the lack of an existing product. This is what I had to do for a clock for my apartment:

http://www.youtube.com/watch?v=Phde6ZmdWJcSecond: There do exist (somewhat) reasonably priced analog 24-hour clocks, for Earth time. If you use one of these and slow it down for Mars time, you will then have a clock showing Mars hours, minutes, and seconds. You can find them on eBay; just search for

"24 hour" clock (with quotes around "24 hour").

Third: Someone already is making (has made?) a watch to handle Mars time, albeit with imperfections. Please see:

http://forums.adafruit.com/viewtopic.php?f=25&t=35102&start=0Fourth: If you are going for mean Mars solar time (1 Mars day = 24 h 39 min 35.244 sec Earth time = 1.027491252 Earth day = 88775.244 Earth seconds, or to put it another way, 1 Earth day = 0.973244296 Mars day), then the only "floating point" arithmetic you need is a single division (or multiplication) by a number close to 1. You don't even need that, really. For example, instead of calculating this

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`x / 1.027491252`

or this

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`x * 0.973244296`

you can calculate this, in integer arithmetic, and it will come out just about the same:

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`x - (x / 37) + (x / 3686)`

or if you want to truly meticulous, use this:

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`x - (x / 37) + (x / 3686) + (x / 38400000)`

(Note: The accuracy of this approach is as least as good as, and probably better than, that of just taking an analog Earth clock and slowing it down.)

Fifth: It is

NOT simple to convert your

local Earth time to Mars time. This is because Mars does not observe Daylight Saving time, but much of Earth does, which throws off your calculations during your region's Daylight Saving Time. If you want simplicity (and I'm sure you do), start with Universal Time (a.k.a. Greenwich Mean Time) and then convert to Mars time.

Sixth: The Chronodot is A-OK. I have one on my clock. This way, I don't need radio signals.

Seventh: If your math skills suck, find someone with decent math skills to help. That can make this kind of work a lot easier.