Tape provides an on-screen "tape measure" for determining and setting distances. The tape is composed of two named objects, in the same way targeted lights and cameras are. By default, these are named Tape### and Tape###.Target (the ### is a three-place number). The tape and target icons are connected by a line representing the current distance between them.

Using a tape helper to measure the distance from floor to window frame.
You can drag a length (the default), or enter a specific length by turning on Specify Length. You can snap or align either end of the tape or link to objects in your scene. Deleting either end deletes the tape.
You can select a tape-measure object from either end, or from the middle. When you click the connecting line, both ends of the tape object become selected so you can move them as one. Note that the same is true of target cameras and lights.
To measure a distance:
The distance between tape and target appears in the Length field. The number in the Length field is gray to indicate that this is a read-only measurement.
 Move either end to a new location. The line between stretches to the new distance, shown in the Length field.
 Move either end to a new location. The line between stretches to the new distance, shown in the Length field. To set a distance:
The connector line is the length you specified, although you can still set the target to any offset by dragging. You can reorient this line as required.

Specifies the length of the tape object. You must select the Specify Length checkbox to enable this option.
Activates the Length parameter setting. Otherwise the tape object's length will be specified by clicking and dragging in the viewport.
Displays the angle of the tape object relative to each axis in world space.
Displays the angle of the tape object relative to each of these home planes.