Exactly what does this do. Can you use it to determine the distance from the lands for a given bullet? A friend said he saw one in a reloading shop in my old home town and ask me about it, but I couldn't tell him a darn thing. Thanks ... Tom P

It's basically a micrometer that you put the brass or loaded round in. I like them for measuring shoulder set back. You can also get the base to Major diameter of the bullet meas. on a loaded round. It gives you a comparative measurement rather than inches, etc.
P.S. Forgot about the little thing that you use to determine bolt-head to rifling. You set that and then measure in precision-mic and record that measurement to compare against loaded rounds for distance from rifling.

I have found it a valuable tool for my .223 in measuring a fire formed round and using these measurements to set the full length sizing die to eliminate headspace as much as possible.

The fake bullet tool is useless as my rifle will not grip the plastic base of the "round" to extract it. I have customised this step using a Dremmel to cut a slot in the neck if an empty case. I place a bullet of the type I am reloading into the neck of this Dremmeled case (unprimed and un-powdered) at excessive length. It is chambered and extracted. I then measure it with the seating piece of the Precision Mic and use an average (average of several chambering exercises) measurement to seat my bullets.