An end effector is disclosed. The end effector comprises a first jaw member comprising a magnetic sensor； a second jaw member pivotally coupled to the first jaw member such that the first jaw member is pivotally moveable between an open position and a closed position, wherein the second jaw member is configured to receive a staple cartridge therein； a staple cartridge removably coupled to the second jaw member, the staple cartridge further comprising an upper surface facing the first jaw member； and a magnet positioned to be in an opposing relationship to the magnetic sensor when the first jaw member is in the closed position. The magnetic sensor is operable to detect the magnetic field of the magnet, and wherein the detected magnetic field is indicative of the distance between the anvil and the staple cartridge.
