A calibration device provides a lightweight rigid support for a long arm. The rigid support includes thin flat sheets separated by a light weight filler. The filler prevents wrinkling or rippling of the flat sheets. Three ball trihedral nest kinematic mounts may be attached to opposite ends of the long arm for precise mounting of retro-reflectors for optical calibration, or precision spheres may be attached to the opposite ends of the long tube to obtain a mechanical calibration standard.