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  1. Calibrate using the normal process and standard .vsk files (see Calibrate cameras).
  2. Set the origin using a standard calibration object (see Setting the volume origin).
  3. In Evoke, create an object for the markers of the custom calibration object (for details, see Create basic objects).
    Do not save this object: it is important that the object that is used for this scaling is created from the current marker observations.
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  4. In the Tracking panel, ensure the custom calibration object is selected, right-click and then click Use for Camera Calibration.

    The Calibration Scaling dialog box is displayed . If and you are alerted that the origin of the selected object is not will be set to the global origin (0,0,0) , you are warned that the object's origin will be set to the global origin when you click Save.

  5. In the Calibration Scaling dialog box:
    1. In the Current Settings section, check that the Selected Wand is the correct wand for your calibration, and that the Selected Object is also correct.

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    2. Ensure the custom calibration object is enabled, then select a pair of markers that correspond to a measurement that you took earlier, and click Add Measurement.
      A line is added to the table containing the Model Distance, which is the distance between the markers as measured by the current Vicon calibration
    3. In the Measured Distance column, enter the distance that you measured in millimeters.
    4. For each set of measurements you have taken from the object, repeat steps b and c.
      In the New Settings section, the scale factor that will be applied is displayed, together with the output names for the scaled wand and calibration objects.

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    5. If you are happy with this measurement, click Save to exit the dialog box.
      A scaled wand and a calibration object file are saved by default to C:\Users\Public\Documents\Vicon\Evoke1.x\CalibrationObjects and are displayed in the Wand and L-Frame lists on the Camera Calibration tab.

      The current calibration is also scaled by the same factor, so you do not need to recalibrate after this operation.
  6. In future, to obtain an accurately scaled volume, use the new scaled wand and calibration object when performing the calibration and set object operations (see Recalibrate with the scaled wand and custom calibration object).