224 Agilent InfiniiVision 3000 X-Series Oscilloscopes User's Guide
14 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.
• N = the number of measurements taken.
-2σ
mean
-1σ 1σ
2σ
68.3%
-3σ
95.4%
99.7%
03σ
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