In agreement with what Ibraheem stated above, Precision and Accuracy are most at risk with aging devices as use brings wear and fatigue. Part 21 CFR 820.72 of the FDA Medical Device regulations defines the rubric for calibration standards. proper calibration is not just dependent on the upkeep of the device, it must be considered during the design process as well. consider an simple caliper for example. a cheap potentiometer, poor sliding mechanisms or locks, or even a misplaced access port that can introduce dust into the system can cause faulty calibration and therefore need for repair. I believe much emphasis should be placed on designing products that require minimal upkeep and minimize part replacement cost so that maintaining FDA standards for calibration is simple and inexpensive for the user.