SPC Statistics Concepts
Standard SPC statistics can be viewed on the Process Trend/SPC and SPC History windows. Standard SPC statistics are defined as:| · | X-Bar Upper Control Limit
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| · | X-Bar Lower Control Limit
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| · | Range Upper Control Limit
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| · | Range Lower Control Limit
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| · | X-Bar Mean
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| · | Range Mean
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| · | Upper Specification
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| · | Lower Specification
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icon. To close the popup window, click on this icon again.
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| · | SPC Graph Area
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| · | Graph Area
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| · | Viewing Actual Values on a Graph
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| · | Viewing Maximum and Minimum Graph Values
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| · | Size Field
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| · | Changing The X-Axis
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| · | Graph Scaling Options
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| · | Manually Scaling Graphs
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| · | Autoscaling Graphs
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| · | Auto Scale Every Cycle
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| · | Cycle
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| · | Cycle Value
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SPC Graph Area
The window displays a line chart of the SPC values collected for a specific process variable. It includes two graphs. The top graph is a plot of X-bar values and the bottom is a plot of the associated range values. The X-axis is the time at which the SPC values were recorded. The number of values graphed may be a subset of the total collected.
To view the maximum value for a graph, click anywhere on the far right-hand side of the window, outside of the graph borders but within the top and bottom lines of the desired graph. To view the minimum value of a graph, click anywhere on the far left-hand side of the graph, outside of the graph borders. To view actual values, click in the middle of the graph area.
Graph Area
The graph area displays a plot of the most recent process variable values. Clicking anywhere within the graph area displays a new window with exact x,y coordinate values. A vertical line marker also appears -- designating the data point selected.
To view the maximum value for a graph, click anywhere on the far right-hand side of the window, outside of the graph borders but within the top and bottom lines of the desired graph. To view the minimum value of a graph, click anywhere on the far left-hand side of the graph, outside of the graph borders. To view actual values, click in the middle of the graph area.
Viewing Actual Values on a Graph
There are two ways to view the exact values of the last 'n' cycles on a graphical window:
| · | Click anywhere within the borders of the graph. A vertical line marker appears -- designating the data point selected. A new window also appears displaying the exact x, y coordinates. The data point selected by the mouse placement is highlighted on the new window.
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| · | Click on the  icon for a table format of a Trend graph.
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| · | For each machine cycle update, the new value appears in the Cycle 1 Value cell, moving older values down sequentially.
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Viewing Maximum and Minimum Graph Values
To view the maximum value on any graph window:
| · | Click anywhere on the far right-hand side of the window, outside of the graph borders but within the top and bottom lines of the desired graph.
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| · | Click anywhere on the far left-hand side of the window, outside of the graph borders, but within the top and bottom lines of the desired graph.
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Size Field
Changes the number of plotted values on the graph.
Changing The X-Axis
The x-axis may be changed from the Size field. The Size field represents the displayable history size for the process history graph or the SPC History size for the X-Bar and Range chart.
To change the x-axis:
| · | Click on the Size field.
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| · | Move the cursor down the selection list to the desired x-axis range.
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| · | Release the mouse button.
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Graph Scaling Options
There are three primary scaling options:
| · | Manual Scale - This option allows you to manually enter the maximum and minimum values for the Y-axis. The Manual Scales window appears when this button is pressed.
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1. Click on the icon.
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| 2. Type in the values you wish to change.
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| 3. To make the changes effective, select the OK button.
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| 4. To cancel any changes made, select the Cancel button.
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| · | Auto scale Once - This option automatically scales the graph when the  button is pressed. The maximum and minimum values for the Y-axis are calculated using the selected data, the high limit, and the low limit. Once these values are calculated, they are retained until this button is clicked again or another scale option is chosen.
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| · | Auto scale every machine cycle - Each window update forces a rescale when the  button is chosen. The graph is always scaled according to the displayed data. The maximum and minimum values for the Y-axis are calculated using the selected data, the high limit, and the low limit.
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Manually Scaling Graphs
Allows you to manually enter the maximum and minimum values for the Y-axis. A new window appears when this button is pressed.
Autoscaling Graphs
Automatically scales the graph when the above button is pressed. The maximum and minimum values for the Y-axis are calculated using the selected data, the high limit and the low limit. Once these values are calculated, they are retained until this button is clicked again or another scale option is chosen.
Auto Scale Every Cycle
Forces a rescale when chosen. The graph is always scaled according to the displayed data. The maximum and minimum values for the Y-axis are calculated using the selected data, the high limit, and the low limit.
Cycle
The actual machine cycle number.
Cycle Value
The actual machine cycle value.