A major point to be emphasized here is the maintenance should attempt to minimize total cost - not just maintenance cost. A second point is that total cost should be what some call “whole body cost,” and include: - unit purchase cost - cost of training personnel to use the unit - cost of buying a replacement at the end of this unit’s lifetime - cost of disposing of the old unit - cost of maintaining the unit during its useful lifetime - cost of upgrading the unit during its lifetime - etc.