By center hole end, I assume you mean the conical end. That is for finding the center of large round stock laid on its side, not for finding center holes. Say you want to mill a key slot or drill a cross hole in a shaft too large for the cylindrical end of the center finder to reach. To center the mill spindle over the center of the shaft, use the conical edge finder. With the spindle turning at around 1000 RPM, approach one side of the shaft at a Z height such that the middle of the edgefinder cone touches the shaft surface. This will be at something like 30 degrees north latitude on the shaft, so to speak. When the cone "kicks" off to the side, zero the Z axis and whichever other axis is perpendicular to the shaft axis. Get clear of the shaft, move to the other side, get back to Z=0, then re-approach the shaft from the opposite direction. Note the reading on the other axis when the cone kicks. The center of the shaft will be exactly half the reading on this axis. In essence, you have taken the average of the position readings on two sides of the shaft. You can see why it is critical that both sides be touched at the same Z height.