Remote indicating systems for mine roof supports

Claim 1

A MINE ROOF SUPPORT INCLUDING HYDRAULIC JACK MEANS AND A MEMBER MOVABLE BY SAID HYDRAULIC JACK MEANS RELATIVELY TO A STATIONARY PART OF THE SUPPORT, A CASING FIXED ON SAID STATIONARY PART OF THE ROOF SUPPORT AT A POSITION OUTSIDE SAID JACK MEANS, AN ADJUSTABLE ELECTRICAL POTENTIOMETER UNIT HOUSED IN SAID CASING, MEANS OPERATIVE TO ADJUSTING SAID POTENTIOMETER INCLUDING AN EXTENSIBLE AND RETRACTABLE PART WHICH EXTENDS OUT OF SAID CASING, MEANS ON SAID EXTENSIBLE AND RETRACTABLE PART CONNECTING IT TO SAID MEMBER WHEREBY SAID PART OF THE POTENTIOMETER ADJUSTING MEANS IS EXTENDED OR RETRACTED SIMULTANEOUSLY WITH MOVEMENT OF SAID MEMBER, AN ELECTRICAL RESISTANCE BRIDGE CIRCUIT WHICH INCLUDES SAID POTENTIOMETER, WHEREBY THE ELECTRICAL POTENTIAL ACROSS THE BRIDGE CIRCUIT VARIES WITH THE ADJUSTMENT OF SAID POTENTIOMETER, AND A GALVANOMETER INSTRUMENT, AT A REMOTE STATION, RELATIVELY TO THE SUPPORT, CONNECTED ACROSS SAID BRIDGE CIRCUIT SO AS TO RESPOND TO SAID ELECTRICAL POTENTIAL AND THEREBY INDICATE AT SAID REMOTE STATION THE POSITION OF SAID MEMBER RELATIVELY TO THE STATIONARY PART OF THE SUPPORT.