This is called the index of variability or "standard deviation."
For each measurement, the coefficient of variation, standard deviation and probable error were computed.
And against the first target the accuracy observed was about .7 mils, in standard deviation.
standard deviation n.
Symbol σ
A statistic used as a measure of the dispersion or variation in a distribution, equal to the square root of the arithmetic mean of the squares of the deviations from the arithmetic mean.
In statistics, a measure of how much the data in a certain collection are scattered around the mean. A low standard deviation means that the data are tightly clustered; a high standard deviation means that they are widely scattered.
Note: About sixty-eight percent of the data are within one standard deviation of the mean.