Standard Deviation Viscosity

quote:

calculating

Dear Rgf12,

From my side, normally if these sampling point is integrated in one forced and cirlulated lubrication system, the oil viscosity shall equal

no need to calculate standard deviation (STDEV) to get viscosity based line. normally we just put limit +/-10% from its original viscosity (Reff: ASTM D 6224)

but for establishing metal wear based limit, STDEV is required

My first cut would to use all the data, unless there is a clearly evident outlier (specific data point, or machine). Calculate the average and standard deviation. I would then throw out the data that exceeds the average +/- 2 standard deviations and re-calculate the new average and new standard deviation. This is an interative process, so you may do it a couple of times. One thing to be concerned about it do you have enough data to be confident that the calculated values represent reality, especially if you are throwing data out of the analysis.

Good luck!