Differential pressure measuring instrument

Claim 1

A PRESSURE RESPONSIVE MEASURING AND RECORDING INSTRUMENT FOR USE IN A BORE HOLE COMPRISING A HOUSING ADAPTED TO BE LOWERED INTO SAID BORE HOLE, MEANS PROVIDING WITHIN SAID HOUSING AN EXPANSIBLE CHAMBER HAVING A PAIR IF WALLS MOVABLE INDEPENDENTLY TO CONTROL THE VOLUME OF SAID CHAMBER, ONE OF SAID WALLS BEING EXPOSED TO BORE HOLE PRESSURE TO VARY THE VOLUME OF SAID CHAMBER, SERVO MEANS HAVING A NORMAL ZERO POSITION AND OPERABLE TO MOVE THE SECOND OF SAID WALLS TO VARY THE VOLUME OF SAID CHAMBER, MEANS SENSITIVE TO MOVEMENT OF THE FIRST WALL TO CONTROL SAID SERVO MEANS TO MOVE THE SECOND WALL TO A POSITION TO CHANGE THE PRESSURE WITHIN SAID CHAMBER TO SUBSTANTIAL EQUALITY WITH THE BORE HOLE PRESSURE, THEREBY TO RESTORE SAID FIRST WALL SUBSTANTIALLY TO A PREDETERMINED POSITION, MEANS SENSITIVE TO A PREDETERMINED LIMIT MOVEMENT OF SAID SERVO MEANS FROM ITS NORMAL ZERO POSITION TO SUBJECT THE INTERIOR OF SAID CHAMBER TO SAID BORE HOLE PRESSURE TO PROVIDE FOR FLOW OF FLUID TO EQUALIZE THE PRESSURE IN THE INTERIOR OF THE CHAMBER WITH THE BORE HOLE PRESSURE, MEANS FOR SIMULTANEOUSLY RESTORING SAID SERVO MEANS FULLY TO ITS ZERO POSITION AND MEANS FOR THEN ISOLATING THE INTERIOR OF SAID CHAMBER FROM THE BORE HOLE PRESSURE, AND MEANS OPERATED BY SAID SERVO MEANS TO RECORD THE POSITION OF SAID SERVO MEANS AND THEREBY PROVIDE A RECORD OF BORE HOLE PRESSURE CHANGES.