HP 54710A User's Reference Manual page 120

Define Measure Menu
Statistics
When you press the Statistics softkey, this second-level softkey menu comes
up on the display.
Off
Stops the statistics measurements, resets the results, and erases the statistics
measurement results from the display.
mean, stddev
Mean and stddev (standard deviation) calculates the mean and standard
deviation of the automatic measurement results. Mean is the statistical
average of all results for a particular measurement. Standard deviation
measures the dispersion of those measurement results
Figure 7-3 shows the mean and standard deviation more graphically.
Standard deviation is represented by the Greek letter sigma (σ). For a
gaussian distribution, two sigma (±1σ from the mean) is where 67 percent of
the data points reside, and six sigma (±3 σ from the mean) is where 99.7
percent of the data points reside.
Figure 7-3
Standard deviations of a gaussian distribution
7–11