I was working on a map and needed to clip my brush. I accidentaly toggled these little dimension numbers when I tried to clip on, a pic is at the link.
http://dhost.info/RabidMonkey777/clipnumbers.jpg
It's a helpful tool, but the usage of it was buried in the Hammer manual, and doesn't look commonly used. It's toggled on/off by pressing o when you have a brush selected in Clip mode. It makes precise clipping a whole lot easier, so for all of you who never knew about it, give it a try.
Hopefully, you'll find this useful.
Happy mapping.
-Rabid