mbf hsg must_be_funny 080831 ... dosquatch meantime_between_failures The amount of time (statistically) you can expect a wear_item to last before it stops functioning. The figure cited is usually 50% mortality, though for critical or high-availability items (medical systems, for instance) PM may be based on a 20%, 10%, 5%, or even lower mortality MBF. That's mortality of the item. To determine a 20% mortality MBF of a lightbulb, for instance, you take 1000 lightbulbs, turn them on, and start a timer. When only 800 of them are still burning, the time elapsed is your MBF. For critical systems, you use lower mortality rates to set your PM (preventative_maintenance) schedule. You actually replace whatever it is (hopefully) well before it goes bad because (again for_instance) you don't want to wait until the blades start coming off your helicopter to do the tune_up. 080831 ... dos crap, and I'm wrong. MTBF, dammit. 080831 ... hsg yeah but you'right because you made a funny! 080831 what's it to you? who go blather from