How to measure blood pressure accurately?

I personally believe that the first measurement should be taken as the second and third measurements on the same side of the arm are affected by venous congestion.

If you want to repeat a blood pressure measurement on the same arm, you should raise your arm after the first measurement to allow venous blood to return and prevent venous blood from influencing the blood pressure measurement.

Also blood pressure is related to a person's exercise condition, such that it is higher after exercise than in a quiet state. It is also related to mood, and blood pressure can be high when you are emotionally stressed.