A dial indicator is a measuring tool. It can measure small distances by detecting small amounts of movement. Most of them look like a watch with a small arm extending. You can get one at the precision tool store. I think Sears even has them. You would want one that reads thousandths of an inch. Once you get one we can advise you how to use it. You can try someting else to see how close you are: See how thick of a feeler gage or shim stock you can get between the teeth.
Jim