It is quite small (10mm x 1 3/4"), has both metric and English scales, and I actually have excess room in the pouch most of the time. I do archaeology and there are times I need measurements when I don't have my full kit. I have found that I have used it a surprising number of times in a variety of other circumstances (measuring pipe diameters, etc). I had to pull it out to provide the dimensions cited above, for instance. Now I will never give it up.

Doesn't everybody carry one?