6. APPARATUS FOR INDICATING AT THE SURFACE THE LENGTH OF CORE IN THE INNER BARREL OF A CORE BARREL AS A CORE IS BEING CUT FROM A SUBTERRANEAN FORMATION COMPRISING ELECTRICAL CIRCUIT MEANS EXTENDING FROM THE SURFACE TO THE CORE BARREL INCLUIDNG INDICATING MEANS AT THE SURFACE RESPONSIVE TO A CHANGING PARAMETER IN THE CIRCUIT AND AN ADJUSTABLE ELEMENT AT THE CORE BARREL FOR CHANGING SAID PARAMETER, SAID ADJUSTABLE ELEMENT HAVING A STATIONARY SECTION AND A SECTION MOVABLE RELATIVE TO THE STATIONARY SECTION TO CHANGE THE OUTPUT SIGNAL OF SAID ADJUSTABLE MEANS; RESILIENT MEANS URGING THE MOVABLE SECTION IN ONE DIRECTION, AN ELONGATED, FLEXIBLE MEMBER CONNECTED TO THE MOVABLE SECTION AND SUSPENDED IN THE INNER BARREL TO EXERT A FORCE ON THE MOVABLE SECTION OPPOSING THE FORCE EXERTED THEREON BY THE RESILIENT MEANS, AND MEANS SLIDABLY MOUNTED IN THE INNER BARREL TO BE MOVED UPWARDLY IN THE BARREL BY THE CORE AS IT ENTERS THEREIN TO INCREMENTALLY COLLECT THE FLEXIBLE MEMBER AND REDUCE THE FORCE EXERTED ON THE MOVABLE SECTION BY AN AMOUNT PROPORTIONAL TO THE DISTANCE THE CORE HAS ENTERED THE BARREL TO PERMIT THE RESILIENT MEANS TO MOVE THE MOVABLE SECTION OF THE ADJUSTABLE ELEMENT AND CHANGE TO OUTPUT SIGNAL THEREOF AN AMOUNT PROPORTIONAL TO THE LENGTH OF CORE IN THE BARREL.