About chart point
- Last UpdatedNov 04, 2024
- 2 minute read
A chart point is a data point or a plot point that can be plotted in a chart. The data for a chart point could be an individual reading or a data calculated from the set of individual readings from one or more samples. When the chart point is derived from a set of individual readings, the calculation for that chart point depends upon the chart type that is linked to a characteristic.
The lower control limit (LCL) and upper control limit (UCL) for a chart point are calculated using the standard deviation (given or calculated). Since the control limits may vary for each chart point in a chart, the control limits are calculated for each chart point in a chart. The calculation for control limits may also vary for each chart type.
The lower sigma (LS) and upper sigma (US) are calculated for a chart point. Finally, the CL, LCL, UCL, LS and US are used to validate a rule violation against a chart point.
The control rules are validated for each chart point calculated based on the chart type against the control limits and sigma calculated for each chart point.
The method to obtain a chart point from each chart type is described in the following table:
|
Chart Type |
Chart Point |
|---|---|
|
Individual Values (ix) |
Individual Reading. |
|
Moving Range (ix + mr) |
Absolute Range between 2 consecutive points. |
|
Moving Range (ma + range) |
Absolute Moving Range among consecutive points, where the number of points is equal to moving average span configured for a characteristic. |
|
XBar (xbar + range) |
Xbar value from each sample. |
|
XBar (xbar + sigma) |
Xbar value from each sample. |
|
Range |
Range value from each sample. |
|
Sigma |
Population Sigma from each sample. |
|
Moving Average (ma + range) |
Moving Average among consecutive points, where the number of points is equal to the moving average span configured for a characteristic. |
|
Moving Average (ma + sigma) |
Moving Average among consecutive points, where the number of points is equal to the moving average span configured for a characteristic. |
|
p |
Fraction Defective, that is, Value/Actual Sample Size. |
|
np |
Defective Count (Value). |
|
c |
Defect Count (Value). |
|
u |
Defects per unit, that is, Value/Actual Sample Size. |
|
DPMO |
Defects per Million Opportunities. |