Precision caliper

Claim 1

A PRECISION CALIPER COMPRISING A SUBSTANTIALLY FLAT YOKE-SHAPED FRAME WITH A FIRST JAW AND A SECOND JAW; A FIXED FLAT STUD ON SAID FIRST JAW; A TUBULAR GUIDE ELEMENT ON SAID SECOND JAW IN LINE WITH SAID FIXED STUD, SAID GUIDE ELEMENT BEING PROVIDED WITH A HANDLE-SHAPED EXTENSION FACING AWAY FROM SAID FIRST JAW; A PISTON AXIALLY SLIDABLE IN SAID GUIDE ELEMENT; A SECOND STUD CARRIED ON SAID PISTON FOR DISPLACEMENT THEREWITH AND FACING SAID FIXED STUD; A PAIR OF JUXTAPOSED FLAT INDICATOR MEMBERS OF LIGH-TRANSMISSIVE MATERIAL WITH A CONTACT SURFACE PERPENDICULAR TO THE PLANE OF SAID FRAME MOUNTED THEREON IN LINE WITH SAID PISTON, ONE OF SAID INDICATOR MEMBERS BEING RIGID WITH SAID PISTON AND BEARING A DISTANCE SCALE AT LEAST PARTLY RECEIVABLE IN SAID EXTENSION, THE OTHER OF SAID INDICATOR MEMBERS BEING FIXED ON SAID FRAME AND BEARING A VERNIER SCALE POSITIONED FOR CO-OPERATION WITH SAID DISTANCE SCALE TO REPRESENT THE SEPARATION OF SAID STUDS; A SOURCE OF LIGHT MOUNTED ON SAID FRAME SEPARATION ADJACENT OF SAID GUIDE ELEMENT WITH SAID EXTENSION FOR TRANSLUMINATION OF SAID INDICATOR MEMBERS IN A DIRECTION SUBSTANTIALLY IN SAID PLANE AND PERPENDICULAR TO THE DIRECTION OF SLIDING MOTION OF SAID PISTON, SAID FRAME BEING PROVIDED IN THE REGION OF SAID SECOND JAW WITH A RECESS ALIGNED WITH SAID SOURCE FOR RECEIVING TRANSLUMINATING LIGHT RAYS THEREFROM; OPTICAL MAGNIFYING MEANS FOR SAID LIGHT RAYS IN SAID RECESS; DEFLECTOR MEANS IN SAID RECESS BEYOND SAID MAGNIFYING MEANS FOR DIRECTING SAID LIGHT RAYS ONTO A PATH GENERALLY PERPENDICULAR TO SAID PLANE; A VIEWING SCREEN PARALLEL TO SAID PLANE CARRIED ON SAID FRAME AT A LOCATION LATERALLY OFFSET FROM SAID GUIDE ELEMENT FOR ILLUMINATION BY SAID LIGHT RAYS UPON THEIR EMERGENCE FROM SAID RECESS; AND CONTROL MEANS ON SAID FRAME IN THE REGION OF SAID SECOND JAW FOR SLIDINGLY DISPLACING SAID PISTON IN SAID GUIDE ELEMENT.