HP 64783A, User Manual

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Error tolerance and
confidence level An approximate error may exist in displayed information.
Error tolerance for a level of confidence is calculated using
the mean of the standard deviations and the mean of the
means. Error tolerance gives an indication of the stability
of the information. For example, if the error is 5% for a
confidence level of 95%, then you can be 95% confident
that the information has an error of 5% or less.
The Student’s "T" distribution is used in these calculations
because it improves the accuracy for small samples. As the
size of the sample increases, the Student’s "T" distribution
approaches the normal distribution.
The following equation is used to calculate error tolerance:
Where:
O
m
Mean of the standard deviations in each time range.
t Table entry in Student’s "T" table for a given confidence
level.
N Number of intervals.
P
m
Mean of the means (for example, mean of the average
times in each time range).
Chapter 7: Making Software Performance Measurements
To use the Software Performance Measurement Tool
300