Final answer:
The diastolic blood pressure is read when the tapping sound through the stethoscope ceases, indicating free blood flow through the artery at the lowest arterial pressure during heart's resting phase.
Step-by-step explanation:
When taking blood pressure, you start reading the diastolic pressure at the moment when the blood flows freely through the artery, and the tapping sound heard through the stethoscope disappears. The diastolic pressure is the lower number of a blood pressure reading, such as 80 in a typical reading of 120/80 mm Hg.
It represents the arterial pressure of blood during ventricular relaxation, or diastole, and is indicative of the elasticity of the arteries in maintaining pressure between heartbeats.