The three-point line is easy to remember and the blood pressure measured is reliable. But the emphasis on the need for a three-point line is unscientific, that is, unjustified. It should be stressed that the cuff is parallel to the atrium, the sphygmomanometer mercury column should be perpendicular to the ground, the reason is simple: the cuff and the connecting tube is filled with gas, not liquid, the physical result of gas conduction pressure is the pressure generated by the gas in the container on the walls of the container are equal, so the sphygmomanometer mercury column zero position has nothing to do with the measurement results. In this conclusion, someone also wrote an article, we can repeatedly verify in the actual work, irrefutable.