ONE SIGMA
This is a statistical value giving precision based upon counting statistics, i.e. count rate and counting time and is calculated from the square root of the total counts. It is sometimes also referred to as a "standard deviation" even though one can calculate a value based upon only one measurement (see Poisson Statistics) Use the one sigma value to evaluate whether a given average count rate represents a homogeneous set of sample data.
Standard deviations (SDEV) larger than the one sigma value (1SIG), i.e., SIGR >1, indicate the possibility of actual compositional variation within the data set. The 1 sigma value is the predicted standard deviation based on the count rate and counting time. It is calculated by dividing the square root of the count rate by the square root of the average counting time.
where : icps = intensity in counts per second
ts = count time in seconds