The little hand held tachs were handy back when. The speeds of different shafts on combines had to be set for the crop. This one is direct reading, you will find others that require you to check revolutions with a watch, also back in the days of overhead line shafts and flat belts, different machines had to be set to a certain speed, to run right. With this one you can check electric motor speed, at farm sales they usually bring no more than five to eight dollars, but thats around here where they aren't scarce.