BACKZ (System Variable)

Stores the back clipping plane offset from the target plane for the current viewport, in drawing units.

(Read-only)
Type: Real
Saved in: Drawing
Initial value: 0.0000

Meaningful only if clipping is specified in CAMERA, DVIEW, or 3DCLIP. If there are several cameras, the value is the last back clipping plane that you set current. The distance of the back clipping plane from the camera point can be found by subtracting BACKZ from the camera-to-target distance.