A sphygmomanometer is a device used to measure blood pressure. The two types of sphygmomanometers are aneroid and mercury. According to "Sustaining Hospitals: Comparing Mercury and Aneroid Sphygmomanometers," both models are reliable, accurate, similar in cost and relatively easy to maintain. Both models should be calibrated frequently to ensure their measurements are accurate. Because of the dangers of mercury exposure, aneroid models tend to be more common. It is recommended that all aneroid sphygmomanometers be calibrated annually against a well-maintained mercury model.
Connect the tubing from each manometer to each side of the plastic T.
Attach the inflation bulb to the bottom of the plastic T.
Inflate the manometers using the bulb to 300mm Hg.
Release the air at a rate less than 10mm Hg per second.
Stop the release at 250, 200, 150, 100, 60 and 0mm Hg and note the reading on both manometers.
Compare the readings. If the readings are within 3mm Hg, the gauge is appropriate for clinical use. If the readings are greater than 3mm Hg apart, the manometer should be discontinued for use until corrected.
Other issues that may arise with your sphygmomanometer are leaks or the pin not resetting to zero. To check for a leak, you can wrap the cuff around itself and inflate it to 250 mmHg. Without releasing the air with the valve, watch the needle to see if it is moving down. If it is slowly moving down, there may be a leak in the cuff, tubing or inflation bulb. If the needle won't reset at zero, you can remove the glass cover and manually lift the needle off the pin and place it back on, lining it up to the zero. Then repeat the calibration procedure to ensure it is appropriate for clinical use.