Lying down and sitting are both clinical ways of measuring blood pressure, and there is no such thing as which is more accurate, as long as the method is correct. When measuring blood pressure clinically, it is required to ensure that the cuff of the sphygmomanometer is at the same height as the heart, so whether you are sitting or lying down, as long as the measurement method is correct, there is no such thing as which one is more accurate. And make sure that the sphygmomanometer cuff is about 2cm above the elbow socket, and the cuff should be loose enough to put in one finger, and the stethoscope should not be put inside the cuff. And take a rest for more than half an hour before measuring blood pressure, preferably without having taken medication that raises or lowers blood pressure, and do not drink strong tea or coffee.