Drawing aid

Claim 1

APPARATUS, FOR USE IN PREPARING A DRAWING, COMPRISING A CIRCULAR TABLE FOR SUPPORTING A SHEET ON WHICH THE DRAWING IS TO BE MADE, SAID TABLE PROVIDE WITH NOTCHES IN ITS PERIPHERY, A RECTANGULAR FRAME, MEANS ROTATIVELY SUPPORTING SAID TABLE AT ITS CENTRE FROM SAID FRAME, A CLAMPING LEVER PIVOTALLY SUPPORTED FROM SAID FRAME, A CLAMPING MEMBER SUPPORTED FROM SAID FRAME, SCREW-OPERATED MEANS FOR MOVING SAID CLAMPING MEMBER INTO CLAMPING RELATIONSHIP WITH SAID TABLE, AN ARM EXTENDING RADIALLY FROM SAID SCREW-OPERATED MEANS, A LINK INTERCONNECTING SAID ARM AND SAID CONTROL LEVER TO MOVE SAID CLAMPING MEMBER INTO ITS CLAMPING POSITION WHEN SAID CONTROL LEVER IS ACTUATED TO ONE SIDE OF A NEUTRAL POSITION, A BAR PIVOTALLY SUPPORTED AT ONE END FROM SAID FRAME, A CAM SURFACE AT THE OUTER END OF SAID ARM, A CAM-FOLLOWER AT THE OTHER END OF SAID BAR, A ROLLER PIVOTED FROM SAID BAR INTERMEDIATE THE ENDS OF SAID BAR, MEANS BIASING SAID CAMFOLLOWER ON TO SAID CAM, SAID CAM WHEN SAID CONTROL LEVER IS AT THE OTHER SIDE OF THE NEUTRAL POSITION PERMITTING SAID ROLLER TO ENGAGE THE PERIPHERY OF SAID TABLE AND ENTER A NOTCH WHEN BROUGHT INTO REGISTRATION BY A ROTATION OF SAID TABLE, A RECTILINEAR GUIDE OF CIRCULAR CROSS-SECTION SUPPORTED FROM SAID FRAME PARALLEL TO A SIDE EDGE THEREOF IN A POSITION LATERALLY CLEAR OF SAID TABLE, A SLIDE MOVABLE ALONG SAID GUIDE, AND A RULE SUPPORTED FROM SAID SLIDE TO EXTEND PERPENDICULARLY FROM SAID GUIDE TO OVER-LIE SAID TABLE, SAID SLIDE ROTATABLE ON SAID GUIDE SO THAT SAID RULE CAN BE RAISED CLEAR OF THE SHEET.