Have a look at the timer in my signature (as posted by Larry above) and feel free to use the source as-is or modify it to suit yourself. It supports 1/100th stops because that was the simplest way of building in drydown correction with sufficient accuracy.

I find when printing that 1/8 stop is quite good enough at moderate grades but if you're printing with hard paper and on your final adjustments, you will sometimes want about 1/20 of a stop adjustment. I do test strips at 1/2 or 1/4 stop intervals and often just guess an exposure to within 0.1 or 0.2 from there and it's good enough.