Hi, we have weekly reports to follow our production data.

One data is the standard deviation of a chemical concentration. The value is obtained in Excel with this formula: PICalcVal($J$2;$B4;$B5;"stdev"; 1; 0;"waspi")), where J2 is the tag, B4 and B5 the start and the end of the week.

I not sure that is correct "mathematically" to calculate a standard deviation on one week long. Does someone know how PI-data link calculates the std deviation ?

Do you think it will be better to calculate the stdev on 8 hours and after, the average of theses stdev for the week?

thanks!

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