By "mean" the common understanding/ usage is average.
If a machine is operating 7, 6, 5, 8, and 9 hours during a week of five shifts; the mean operating time would be 7 hours.
If you mean surgeries, it would be the average length of the surgeries in your sample.
documenting up time can be assigned to operataors, or by putting meters on the equipment that document the time it is under power. audits of production records is another way to try to determine that.
In most quality practice, mean operating time is not an issue, mean time between failures, (MTBF) is.
If you are looking for tool monitoring or broken tool detection repost, thats another area and we'd be happy to assist.
milo
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"I wish to propose ... a doctrine which may, I fear, appear wildly paradoxical and subversive. ...that it is undesirable to believe in a proposition when there is no ground for believing it's true". Bertrand Russell
Mean Operating Time??
