Blood pressure is generally measured in the right upper arm, but blood pressure in the right and left upper arms should be measured at the time of the initial examination. Many studies have found a difference in blood pressure between the right and left upper arms, and this difference is independent of whether the left or right hand is used. About 20% of people have a difference in blood pressure between the left and right arm of >10 mmHg, called inter-arm blood pressure difference, so it is recommended that both left and right upper arm blood pressure should be measured and recorded at the first examination. If the inter-arm blood pressure difference persists >10 mmHg, it is highly suggestive of aortic arch narrowing and upper extremity arterial occlusion. In general the blood pressure in the right arm is usually measured predominantly, and generally the blood pressure in the right upper extremity is higher than that in the left upper extremity. This is related to the anatomical differences between the right and left brachial arteries. The difference between the right brachial artery and the left brachial artery is 2-4 mmHg, because the right brachial artery comes from the first branch of the aortic arch, the unnamed artery, and the left brachial artery comes from the third largest branch of the aortic arch, the left subclavian artery. very few people have similar blood pressure in the right and left hands, or the left hand is higher than the right hand. When there is a persistent difference between left and right upper arm blood pressure, the blood pressure of the upper arm on the side with the higher blood pressure should be measured. Studies have shown that significant differences in left and right upper arm blood pressure are a risk factor for predicting cardiovascular disease. In summary, due to differences in the anatomy of the left and right brachial arteries, blood pressure is usually higher in the right arm than in the left arm and is therefore suitable for long-term measurement.