Indicating for straigness over a long part on a lathe 

pretty much exactly what is says on the tin. on reason I have the indicator where it is, that was not explained in the video, is that the trade off in lessend accuracy almost eliminates the risk of me bumping the indicator with my hand while tightening it with my key. I like to spin with one hand and tighten with the other. It also is easy to see on camera vs using a similar arrangement on the front side of the chuck. you can also more easily make sure to eliminate any cosine error and make sure it is perfectly on center. working of the front of a pin this small is far more difficult, but is easy enough on a larger part. testing repeatability off camera, this combination was good to within seven ten thousandths if an inch (0.0007) which is more than adequate for the task at hand.