Ever wondered what they use those darned dial indicators and magnetic bases for? You may have seen one in your local automotive shop or over at your friend's house and didn't want to let on that you haven't got a clue how to use the darned things.

Basically, dial indicators are used to mic something that is round, like a revolving cylinder. Dial indicators are also usually used in conjunction with a magnetic base. The magnetic base is used to hold the dial indicator in position while it is being used.

Lets just say, for example, that you wanted to measure a main bearing, like a rod journal on a crankshaft. The dial indicator is in a stationary position, with the arm resting on the bearing journal of the crankshaft. As the crankshaft is turned, the dial indicator will tell you if the bearing surface is out of round. As the crankshaft rotates, the dial indicator needle follows the surface of the bearing journal and indicates the roundness of it.

A dial indicator can measure in increments of 1/1000, which means if its 2/1000 out, you can see it. There is a one inch throw with the revolution counter in the dial indicator, so as it turns, it tells you how many revolutions it has gone around.