Except that this has been made by almost any first-grade schoolchild in the netherlands during geography lessons to learn about timezones. Perhaps even Charlotte has learned about it there, the name sounds Dutch.
Even better - cut a slot at the top of weighted faceplate, and mount it in front of a second faceplate with names of cities or countries, as in fungus's version.
That way, when you rotate the clock, only the correct city shows, and you get a numbered faceplate.
I think it's important to point out too that you removed the Minute hand, as rotating it 30 deg to move forward/backward the hour would also move forward/backward the time by 10 minutes. Good show old boy, good show.
Well done. I am a Canadian living in the Uk, and am always making international calls (I'm always counting on my fingers to find out the time differences) I will have to make on of these. Good job.
Here's my own version of it.
That way, when you rotate the clock, only the correct city shows, and you get a numbered faceplate.
Is this your invention ?
I've found the answer.
Nice DIY version though ! =o)