256 Keysight InfiniiVision 3000T X-Series Oscilloscopes User's Guide
15 Measurements
The following figure graphically shows the mean and standard deviation. Standard
deviation is represented by the Greek letter sigma: σ. For a Gaussian distribution,
two sigma (± 1σ) from the mean, is where 68.3 percent of the measurement results
reside. Six sigma (± 3σ) from is where 99.7 percent of the measurement results
reside.
The mean is calculated as follows:
where:
• x = the mean.
• N = the number of measurements taken.
•x
i
= the ith measurement result.
The standard deviation is calculated as follows:
where:
• σ = the standard deviation.
-2σ
mean
-1σ 1σ
2σ
68.3%
-3σ
95.4%
99.7%
03σ