Student's drafting instrument

Claim 1

A PORTABLE DRAFTING INSTRUMENT COMPRISING: A BASE MEMBER HAVING A STRAIGHT EDGE PORTION ADAPTED GUIDABLY TO CONTACT A T-SQUARE OR ANALOGOUS RAIL AND AN ARM PORTION EXTENDING GENERALLY PERPENDICULARY FROM THE STRAIGHT EDGE PORTION SPACED ABOVE THE DRIFTING WORK; A TRIANGLE MEMBER ADAPTED FOR PIVOTAL CONNECTION TO SAID ARM PORTION IN UNDERLYING CONNECTION TO SAID ARM PORTION IN ADAPTED FOR PIVOTAL CONNECTION TO SAID ARM PORTION IN OVERLYING RELATIONSHIP AND HAVING GRADUATED INDICIA LINES FOR USE IN DETERMINING THE RELATIVE ANGULATION OF SAID TRIANGLE MEMBER; AND A COUPLING UNIT PIVOTALLY CONNECTING SAID TRIANGLE MEMBER AND SAID PROTRACTOR MEMBER TO SAID ARM PORTION, INCLUDING A CYLINDRICAL ELEMENT PASSING SLIDABLY AND ROTATABLY THROUGH ALIGNED APERTURES IN SAID TRIANGLE, SAID ARM PORTION AND SAID PROTACTOR MEMBER, A FIXED ABUTMENT ON ONE END OF SAID CYLINDRICAL ELEMENT GENERALLY UNDERLYING SAID MEMBERS, A MOVABLE ABUTMENT ON THE OPPOSITE END OF SAID CYLINDRICAL ELEMENT GENERALLY OVERLYING SAID MEMBERS, AND REVERSIBLY SITUATABLE REGULATING MEANS CONTACTING SAID MOVABLE ABUTMENT AND BEING MANIPULATABLE BETWEEN TWO PORTIONS OF RELATIVE ADJUSTMENT, SAID REGULATING MEANS ACTING TO URGE SAID MOVABLE ABUTMENT TOWARD SAID FIXED ABUTMENT IN ONE POSITION OF RELATIVE ADJUSTMENT FOR FRICTIONALLY LOCKING SAID TRIANGLE MEMBER AND SAID PROTRACTOR MEMBER TO SAID ARM PORTION, SAID REGULATING MEANS SERVING TO FREE SAID TRIANGLE MEMBER AND SAID PROTRACTOR MEMBER AT LEAST PARTIALLY FROM SAID FRICTIONAL LOCKING IN A DIFFERENT POSITION OF RELATIVE ADJUSTMENT.