Distance measurement
To measure a linear distance in a 2D or a 3D viewer:
Click Measure in the menu bar.
Click Distance 
. Alternatively, press [M].
Click the first point.
Notes
Right-click to cancel.
For a measurement on a 2D image that has not been calibrated, the calibration starts.
Click the second point.
The point-to-point measurement is shown in the viewer and added to the Annotation tab 
of the smart panel under the group of Measurements or 2D Measurements depending on whether it is a 3D or 2D measurement.
Editing a distance measurement
To edit the distance measurement, drag the control points. The value is updated accordingly.
To move the label of the distance measurement, drag it.
Deleting a distance measurement
To delete the distance measurement, select the measure object in the viewer, and press the Delete key.