A tape measure is used for measuring distances and angles. The world (scaled) length of the tape is displayed in a readout and in a length field on the toolbar. The angle of the tape relative to the +x-axis is displayed only on the toolbar.
Since a tape measure is a track, it has a track menu that is accessible in the Tracks menu on the menu bar or by right-clicking the main video view.
A calibration tape is a tape measure which can be used to calibrate the video scale. For more information, see calibration stick.
To create a tape measure, click the Create button 
and choose Measuring Tools|Tape Measure from the popup menu. You can create as many as you need.
The new tape measure is initially placed slightly above the center of the video image.
To measure distances, drag either end of the tape. To move the entire tape as a unit, drag the middle.
By default, the tape measure has a fixed position--that is, the position of both ends is the same in all frames. Uncheck the Fixed Position checkbox in its track menu to allow the position to vary independently from frame to frame.
Locking the tape measure prevents any changes in its end positions. Lock the tape by turning on the Locked property in its track menu.
Note that if the scale of the video changes, the tape readout will show a different world length even though the end positions of the tape have not changed.