Calculate a monthly OEE

Q: My boss wants me to calculate and present a graphical OEE representation on a monthly basis. I present this as I do with the daily data. I calculate the monthly OEE  by taking the average of the daily OEE’s.

Is it alright to present a monthly OEE of the machines by calculating the average of the daily OEE’s in a month?

Arno Koch •  No. Taking 20 OEE numbers, adding them and dividing by 20 does NOT give a correct OEE number.

OEE is a weighted average. To calculate OEE over a longer span of time you will need to recalculate the whole equation as if it was one OEE.

So calculate the availability over the whole time-span, the performance, the quality and (re)calculate the OEE.

Unfortunately not all OEE software does this correct, leading to wrong conclusions.

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