Patent ID: 8384890

Claim:
Apparatus for measuring the inner surface of a structure embedded in the ground and defining a tunnel, said apparatus comprising a portable stand adapted to be supported by a bottom portion of said structure and projecting upwardly into said tunnel, a rotor supported by said stand for rotation on a generally horizontal axis and having a support surface, a portable battery powered laser unit mounted on said support surface of said rotor and having means for emitting a laser beam and for determining and displaying a distance from said laser unit to a target on said inner surface of said structure, said rotor and said laser unit being rotatable together on said axis to predetermine angular positions around said axis to provide for obtaining a distance measurement reading from said laser unit to said target on said inner surface at each of said angular positions, said rotor comprising a disk having a generally vertical surface, and said laser unit is releasably connected to said vertical surface, said disk having peripherally spaced notches corresponding to angular degrees of rotation of said disk, and a latch member supported by said stand and positioned to engage each of said notches for holding said disk and said laser unit at a selective angle of rotation during a reading of said distance at each of said positions.