The current electronic oscillometric sphygmomanometers are very advanced, their technical requirements on the operator are small, the possibility of error is small, so in general, electronic sphygmomanometers are more accurate. Because the use of mercury sphygmomanometer operator requirements are higher, the sphygmomanometer must be placed flat, and the cuff binding position, the heart position is at the same level, the measurement of the measurement of the line of sight and the mercury column flush, and the brachial artery auscultation to be accurate, cuff deflation can not be too fast or too slow. However, electronic sphygmomanometers often have a limited measuring range, and if the blood pressure is too low or too high, sometimes there will be a measurement error and no readings, which will require the doctor to use a mercury sphygmomanometer to measure.