Patent ID: 7665223

Claim:
A measuring device comprising: a cable including: a midsection; and a free end for placement by a user at a point being measured; a base unit including: a base; a first carriage including: a first frame rotationally attached to said base so as to be rotatable about a first axis; a second carriage including: a second frame rotationally attached to said first frame so as to be rotatable about a second axis; a main datum passage attached to said second frame for confined passage of said midsection of said cable; an angular displacement sensor attached to said second frame defining an alignment position between said main datum passage and said cable free end wherein the local longitudinal axis of said cable is aligned with said datum passage; said angular displacement sensor for sensing angular displacement of said cable out of the alignment position and for producing a displacement signal indicative thereof; a first motor coupled to said first frame for rotating said first carriage about the first axis responsive to the displacement signal from said angular displacement sensor indicative of cable displacement about the first axis so as to move said angular displacement sensor toward or to the alignment position; a second motor coupled to said second frame for rotating said second carriage about the second axis responsive to the displacement signal from said angular displacement sensor indicative of cable displacement about the second axis so as to move said angular displacement sensor toward or to the alignment position; cable measuring means attached to said second frame and coupled to said cable for measuring the length or change of length of said cable and for producing a cable signal indicative of the distance to the point being measured; first carriage measuring means for measuring the rotational position or change of rotational position of said first carriage relative to said base and for producing a first-carriage signal indicative of the angle about the first axis to the point being measured; and second carriage measuring means for measuring the rotational position or change of rotational position of said second carriage relative to said first carriage and for producing a second-carriage signal indicative of the angle about the second axis to the point being measured.