As applied to tubular products, the center of the inside diameter differs from the center of the outside diameter indicating wall variation. This is a problem associated with seamless tubing.
In High Intensity Discharge lamps the Bulb to Arc Angle is the angle off of center between electrodes and bulb. The Bulb to Base Angle is the angle off of center that the bulb is from the base.
A characteristic of seamless tubing in which wall thickness is not consistent throughout the tube.