# Viewing Statistical Results

1. Select a controller in the Plant Structure workspace and then select Statistics in the menu bar.

2. After calculating the statistics, the statistical results can be viewed in the Results tab.
   The statistical results are displayed by different charts: HISTOGRAM, XBAR-R, and XBAR-S.

   The statistics result is not stored on the controller or in ToolsTalk 2, but ToolsTalk 2 holds up to 10 of the latest statistical results per controller in memory.

## Histogram

The histogram chart shows the frequency of the monitored aspect for a number of classes, together with the target, a Normal Distribution curve and a number of limits.
The histogram is a series of bars, each proportional in width to the range of values within a class and proportional in height to the number of samples falling in the class. A histogram reveals the amount of variation that any process has within it. The histogram is useful because it emphasizes and clarifies trends that are not readily discernible in tables.

Legend Item | Description
--- | ---
Normal Distribution | A Gaussian curve calculated from the samples collection. Shows the theoretical distribution of the samples, based on statistical calculations and probability.
Mean | The overall mean value of the samples collection.
+/- 3 Sigma | Part of the definition of the Normal Distribution, stating that 99.7% of the samples collection is expected to be between +/- 3 standard deviations from the Mean value.
Target | The tightening program target value.
Tolerance limits | Defined in the SPC Variable Configuration.

## XBar-R

The XBar-R control charts show both the mean value (XBar) and the range (R) for each subgroup. This is the most common type of control chart using indiscrete or continuous values. The XBar part of the chart shows any changes in the mean value of the process while the R part shows any changes in the dispersion of the process.
This chart is particularly useful because it shows changes in mean value and dispersion of the process at the same time, making it a very effective method for checking abnormalities in the process.

Legend Item | Description
--- | ---
Mean | The overall mean value for the samples collection.
Control limits | Defined in the SPC Variable Configuration. Can be auto-calculated or manual.
Target | The tightening program target value.
Centerline | The mean range of the subgroups.

## XBar-S

The XBar-S control charts show both the mean value (XBar) and the standard deviation (S) for each subgroup.
The XBar-S chart is identical to the XBar-R chart except that the XBar-S shows the standard deviation instead of range.

Legend Item | Description
--- | ---
Mean | The overall mean value for the samples collection.
Control limits | Defined in the SPC Variable Configuration. Can be auto-calculated or manual.
Target | The tightening program target value.
Centerline | The mean range of the subgroups.

## Calculated Statistical Values

A number of calculated statistical key values are displayed in information boxes below the histogram, the XBar-R chart, and the XBar-S chart.

The calculated statistical values are:

- Min = minimum value for all collected sample values

- Max = maximum value for all collected sample values

- Mean =

- Mean+3Sigma = + 3*stdDev

- Mean-3Sigma = - 3*stdDev

- Cp (in XBar-R chart the value is based on range, and in XBar-S chart the value is based on sigma)

- Cpk (in XBar-R chart the value is based on range, and in XBar-S chart the value is based on sigma)

- Center line = in Range part , and in Sigma part

- Target (if available the target value for the monitor)

- Standard deviation = Total overall standard deviation = stdDev