# Configuring SPC Variables

1. On the home view, go to the Reports tab and select Statistics on the left pane.

2. Select the plus icon in the upper-right corner of the screen.
   The SPC Variable window shows the new variable.

3. In the Name box, enter the name of the variable.
   The name of the variable is the heading of the SPC Variable window.

4. Select Tightening Program.
   The Tightening Program window appears and lists all the multistep tightening programs stored in the controller and available for statistical calculations.
   Select the multistep tightening program of the new variable.

   The Tightening Program must be a multistep program.

5. Select Virtual Station.
   The Virtual Station window appears.
   Select the Virtual Station which the results are made from.

   Statistics are based on results made by a Virtual Station that has the following license type assigned:

   - Process Control

6. Select Monitor.
   The Monitor window appears.
   Select one of the following program monitors which the SPC calculation is based on:

   - Step monitor peak torque

   - Step monitor angle

   - Final torque

   - Final angle

   - Program monitor torque

   - Program monitor angle

   When selecting Step monitor peak torque or Step monitor angle, in the Step number box enter the number of the necessary step of the tightening program from which to read the value.

   Use result reporters to have an effect on the following monitor values: Final torque and Final angle.

7. Select Edit limits.
   The Variable configuration window appears.
   For calculations and analysis of the results, set the following limits for each value of interest.

In the Tolerance limits window, set the following limits (used for calculation of the process capabilities Cp and Cpk):

- Upper Tolerance Limit (UTL): a user-defined quantity that identifies the highest acceptable value of a product attribute.

- Lower Tolerance Limit (LTL): a user-defined quantity that identifies the lowest acceptable value of a product attribute.

In the Control limits window, enable or disable the Auto calculate switch.
If the Auto calculate switch is set to Yes, the control limits are automatically calculated.
If the Auto calculate switch is set to No, set the following limits:

- Mean - Upper control limit: a statistically determined measurement that appears as a horizontal dashed line above the process average.

- Mean - Lower control limit: a statistically determined value that appears as a horizontal dashed line below the process average.

- Range - Upper control limit: a statistically determined measurement that appears as a horizontal dashed line above the process average.

- Range - Lower control limit: a statistically determined value that appears as a horizontal dashed line below the process average.

- Sigma - Upper control limit: a statistically determined measurement that appears as a horizontal dashed line above the process average.

- Sigma - Lower control limit: a statistically determined value that appears as a horizontal dashed line below the process average.

In the Capabilities window, set the following limits:

- Cp: the Cp index gives the process capability: it is 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 Cpk index gives 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.