This month marks the 25th installment of ASSEMBLY's X-Y-Z column. During my interviews with suppliers of motion control technology over the past 2 years, I often heard the same complaint: Many manufacturing engineers are confused about certain motion control terms. "If you could teach engineers the difference between accuracy and repeatability," one supplier quipped, "you'd be doing a great public service."

To be fair, suppliers of motion control technology do little to help their cause. For example, the accuracy specification for a multiaxis positioning system rarely states that the figure is for each axis, not all of them. Moreover, the specification may not reflect the system's performance under load.