I think there is no one 'right' way, it all depends on the job. The centres approach works ok if you are trying to centre a flat end face but might not work if the item has any shape on the surface. JohnS' approach works well and i use it, especially if you want to reduce square to round or the surface finish is so poor that a DTI would give fluctuating readings. A DTI approach works well in most circumstances but involves a little more setup effort in getting the DTI out and in position, and is the only truely viable approach when you want to centre a bore in the chuck irrespective of the external shape and particularly when the bore isn't central with respect to the outside edges.