The correct method for measuring blood pressure using a mercury sphygmomanometer.

Using a mercury sphygmomanometer to measure blood pressure is a classic and accurate method. The correct procedure is as follows:

1. Preparation: Ensure the environment is quiet. The patient should rest for 5-10 minutes before measurement and avoid strenuous exercise, smoking, or consuming stimulating beverages such as coffee. The patient should sit in a comfortable position with back support and feet flat on the floor.

2. Inspection and application of the device: Turn on the sphygmomanometer and check whether the mercury column is at the "zero" mark; if not, calibrate it. Remove the sleeve to expose the right upper arm, rolling it up to the armpit to fully expose the arm. Apply the cuff to the subject's upper arm, positioning it at heart level. The tightness should allow space for two fingers to fit comfortably. After locating the brachial artery (on the inner side of the upper arm, upper one-third portion) by feeling the pulse in the elbow fossa, place the diaphragm of the stethoscope over the brachial artery.

3. Reading and recording: During the blood pressure measurement, as the mercury column gradually declines, the reading corresponding to the first clear pulsation sound heard (i.e., Phase I of Korotkoff sounds) represents the systolic blood pressure. Continue releasing the air pressure until the sound completely disappears (indicating the end of Phase IV of Korotkoff sounds), and the reading at this point corresponds to the diastolic blood pressure.