As you let the air out of the cuff, listening with a stethoscope, when you first hear the heartbeat (pulse), that’s the top number or systolic pressure. When the pulse can no longer be heard, that is the second number, or diastolic pressure. The systolic pressure number is the pressure of the heart pumping; the diastolic number is the residual pressure in the arteries. 120/80 is considered an average normal for younger people. It usually goes up a bit in older people.

systolic over diastolic
usually 120/80 is considered normal.
References :
As you let the air out of the cuff, listening with a stethoscope, when you first hear the heartbeat (pulse), that’s the top number or systolic pressure. When the pulse can no longer be heard, that is the second number, or diastolic pressure. The systolic pressure number is the pressure of the heart pumping; the diastolic number is the residual pressure in the arteries. 120/80 is considered an average normal for younger people. It usually goes up a bit in older people.
References :