Before you add your first measurement annotation, you must calibrate the drawing to set the default scale. The calibration is personal to each user and unique to each drawing version.

When you calibrate or recalibrate the drawing, existing annotations and previous revisions aren't affected by the new default scale. For each annotation, you can also change its scale, which doesn't affect the drawing calibration.

See the following example.

To calibrate or recalibrate the drawing:

1. On the Annotation toolbar, select (Measurement) > (Calibrate).
2. Select the drawing and draw a line.
3. If needed, adjust the length and position of the line.
4. In the Calibrate dialog, enter the value, and select the unit of measurement.
   Note: The value must be greater than zero.
5. Select Set.