The tightness of the cuff of the sphygmomanometer has an effect on the measurement of blood pressure. When the cuff is tied tightly the blood pressure measurement will be lower than the true value, while when the cuff is tied too loosely the blood pressure measurement will be higher than the true value. Why does this result? Because when the cuff is tied too tightly, the pressure on the artery increases so that the measured blood pressure is lower than the actual blood pressure, and when it is tied too loosely, the cuff expands in a circular shape after inflation, reducing the contact area with the upper arm, so that the measured blood pressure is higher than the actual blood pressure. If the cuff is tied too tightly, the measured systolic and diastolic blood pressure will be low, and if it is tied too loosely, the blood pressure will be high, and the tightness is generally considered to be the most appropriate when it can fit two fingers.