How do I know if my aneroid or mercurial sphyg is out of calibration?

Aneroid sphygs utilize mechanical gears and a mechanical linkage which can wear out or be knocked out of calibration. ADC aneroids are designed to provide a visual indication of accuracy. Our aneroid will require re-calibration if the indicator needle is outside the oval at the bottom of the dial. Unfortunately, when the needle is inside the oval, you can't be absolutely sure that the gauge is in calibration, unless it is a brand new unit from a reputable manufacturer (that's because gauges can be tampered with - some more easily than others). As such, it's a good idea to periodically test the gauge against a unit of known accuracy, or return the unit to ADC for complimentary testing. How often you should perform these accuracy tests depends on many factors, but in general, once a year should be sufficient.

Mercurial sphygs utilize gravity and contain no moving parts other than the mercury itself. As a result, there is nothing to wear out. A properly designed mercury manometer will be in calibration as long as the meniscus (top of the mercury column) rests within 3mmHg of the zero point with no pressure applied (inflation system should be detached since it might contain residual air). Mercury units do require some maintenance to remain in tip-top shape. Since mercury will evaporate, a small amount might need to be added to the instrument from time to time. Additionally, mercury will oxidize, leaving a residual gray deposit on the inside of the cartridge tube. This should be swabbed away using alcohol applied to a pipe cleaner. Once a year or so, the damping filters and diaphragm located in the top cap above the cartridge tube should be replaced. ADC provides self maintenance manuals with every mercury unit purchased. Of course, we will perform complimentary maintenance on any ADC mercurial manometer returned to our repair facility.