Working with Markups > Measurements > 3D Measurements > To Measure Distance
  
To Measure Distance
1. Click Markup > Distance. The Measure Distance dialog box opens.
2. Select the first reference entity.
3. Press CTRL+Select the second reference. The distance value between the two entities appears in the graphics area and in the Results pane of the Measure Distance dialog box.
4. If you select only point type references, press CTRL+Select repeatedly to select more than two references. The distances between the points appear in the graphics area and in the Results pane of Measure Distance dialog box.
5. Click . The measurement is saved to the annotation set.
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If you click Close before you save the previewed measurements, a warning appears.
Select from the following options:
• To delete, select Discard the measurements
• To save, select Retain the measurements in the view
To set the default for all future measurements in this session, select Do this automatically in the future.
Click OK.