The study of shaft centerline plot from plotting to analyze has been researched extensively by Bently Rotor Dynamic Research Corporation, an extensive work has been carried out by Dr Agnes Muszynska, Don Bently, Bill Pryor, and many others that have contributed to the understanding and analyzing of shaft centreline plots. Shaft vibration amplitude (direct unfiltered), frequency, phase information, and shape or form of timebase/orbit provides the vibration analyst with significant information concerning the overall mechanical integrity of a machine. Additional information is contained in data which relates average radial shaft position to bearing clearance. Yet, often times this important information is overlooked. Typically Overall vibration amplitude is used as the sole indicator of machine acceptability. Most of us intuitively relate high indications on vibration monitors with a potential machine malfunction. Conversely, we usually assume that low vibration amplitudes indicate acceptable mechanical performance. In most cases, this is a correct assumption, but you should not be lulled into a false sense of security. Just the opposite case may be true.
Faisal Youssef (Wed,) studied this question.