Disabling and enabling the three sigma threshold during a PAAT session
The three sigma threshold is a value that represents the mean plus three times the standard deviation. Any residual value that is greater than the three sigma threshold is very likely to be an outlier. The point should be revisited to determine whether it needs to be reread or made inactive.
Any points with total residual values more than three sigma above the mean are flagged in the PAAT Results dialog box. Disabling the three sigma threshold allows you to include points with residual values greater than the three sigma threshold value.
 Start a PAAT session.

Click the Show Results button on the Positional Accuracy Assessment toolbar.
The Positional Accuracy Session Results dialog box appears.

Check and uncheck the Use check box to see how the results are affected when points with large residuals are withheld from the calculation.
Unchecking the Use check box removes the Total Residual value for the selected point from the calculation of the 3 Sigma, Mean, Standard Deviation, Absolute CE, Relative CE, and RMSE values.
 Click Close.