Final answer:
The manometer for measuring arterial blood pressure should be placed at the level of the right atrium, which corresponds with the level of the heart, for accurate readings. Mercury manometers are preferred due to their compact size and convenience.
Step-by-step explanation:
A manometer used to measure arterial blood pressure should be placed at the level of the heart to ensure accurate measurements. Specifically, when measuring central venous pressure or similar parameters, the manometer should be at the level of the right atrium, which is the reference point for pressure in the systemic circulation. In routine blood pressure measurements, an inflatable cuff is placed on the upper arm at the same level as the heart. The arm should be at heart level whether sitting or standing to avoid adding the weight of the blood column that would occur if the arm is higher or lower than the heart. Mercury manometers are commonly used because mercury's high density allows for a shorter column and more convenient readings compared to a water-based manometer.