# Configuring SPC Variables

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

2. The Variable Configuration section contains a list of a Variable Configurations.

   - To create a Variable Configuration, select Add... at the upper-right corner of the section.

   - To delete a Variable Configuration, select the configuration (you can also select more than one configuration) and then select Modify > Delete at the upper-right corner of the section.

   - To update a Variable Configuration, double click the configuration.

Variable Configuration
Information | Description
--- | ---
Name | The name of the variable.
Virtual Station | The Virtual Station that the tightening results are generated from.
Tightening Program | The multistep tightening program of the variable. The Tightening Program must be a Multistep Program.
Monitor | Select the aspect of the tightening result you want to monitor in the calculation: Step monitor peak torque Step monitor angle Final torque Final angle Program monitor torque Program monitor angle If the user uses the result reporters, it is possible to have an effect on the following monitor values: Final torque and Final angle.
Step Number | Specifies the step number. (Only available when Step monitor peak torque or Step monitor angle is selected for Monitor.)

Set the following limits:

Tolerance Limits
Information | Description
--- | ---
Lower Tolerance Limit | Lower tolerance limit for monitored value. Used for calculation of Cp, Cpk values as well as for tolerance limits rendering in SPC results charts.
Upper Tolerance Limit | Upper tolerance limit for monitored value. Used for calculation of Cp, Cpk values as well as for tolerance limits rendering in SPC results charts.

Capabilities
Information | Description
--- | ---
Cp | The process capability. The number of times the spread of the process is into the tolerance width (Upper tolerance limit - Lower tolerance limit). The higher the value of Cp, the better the process.
Cpk | The process capability corrected for the position. It is not useful having a high Cp index if the process setting is way off center in relation to the middle of the tolerance range. A high Cpk index means, then, that you have a good process with a small spread in relation to the tolerance width, and also that it is well centered within that width (Upper tolerance limit - Lower tolerance limit). If Cpk is equal to Cp, the process is set to produce exactly in the middle of the tolerance range.

Control Limits
Information | Description
--- | ---
Auto calculate | If set to On, the control limits are automatically calculated. If set to Off, set the following limits: Mean Range Sigma
Upper control limit | Upper control limit for calculated subgroup values. Used for limits rendering in SPC results charts.
Lower control limit | Lower control limit for calculated subgroup values. Used for limits rendering in SPC results charts.