Fixed two bugs with parseClockFormat.

Apparently log10 isn't supported everywhere, furthermore, using log is
not a great idea due to rounding issues:
 jeremy ~$ node
 > Math.log(1000) / Math.log(10)
 2.9999999999999996
 >

Also, we don't allow the user to specify more than 3 decimal places.
Instead of round name, we're just showing a number now. This is less
pretty, but gives us some precious real estate back.