Rockwell Automation FactoryTalk Historian SE ProcessBook 3.2 User Guide - Manual (Page 169)

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Visualize Data with Symbols
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To calculate b, the following equation is used:
Once m and b are known, the value of y that intersects the best-fit line can
be calculated.
Correlation Coefficient
The Correlation Coefficient (r) varies between -1 and +1. Positive values
indicate that as X increases, Y also increases. Negative values indicate that
as X increases, Y decreases. A value of zero indicates no correlation in the
way the sets of values vary.
The Correlation Coefficient for a set of points is calculated using the
following formula: (n is the number of points, s is the standard deviation).
You can display the correlation coefficient in the plot legend.
Bad data points are not included in this calculation.
Standard deviation(s) is calculated using the following formula:
The mean is the arithmetic average.