Genec had it pretty close. It is a thickness gauge, and yes you can set the zero point on it and use it all day in production or QC work. I have one, though it is not quite as nice as the one in the photo. Anyway, I rarely use it, but they are quick and easy to use. Maybe as I get my new shop space set up I will have a better place to keep it and will get more use out of it. Most of the time now I just use a dial caliper.