Chesapeake Black 2 Water Pressure Gauge 30 PSIPerimeter-lighted Black dial with stylish Blue and White graphics, polished stainless steel bezel, contoured White pointer and domed glass lens.A pressure gauge operates by sending a low amperage current through the gaugess meter to ground via a sending unit with variable resistance. The resistance of the sending units increase or decrease with the changes in pressure, temperature, etc...As the senders resistance varies, the amount of current allowed