An open-end mercury manometer is connected to a low pressurepipeline that supplies a gas to a laboratory. Because paint wasspilled on the arm connected to the line during a laboratoryrenovation, it is impossible to see the level of the manometerfluid in this arm. During a period when the gas supply is connectedto the line but there is no gas flow, a bourdon guage connected tothe line downstream from the manometer gives a reading of 7.5 psig.The level of mercury in the open arm is 900mm above the lowest partof the manometer.