One should therefore take the arithmetic mean as the sum.

必须取算术平均作为和。

standard deviation of the arithmetic mean of a series of measurements

测量列算术平均值的标准（偏）差

standard deviation of the arithmetic mean of a series of measurements

测量列算术平均值的标准（偏）差

standard deviation of weighted arithmetic mean

加权算术平均值的标准（偏）差