During blood pressure measurement, the reading must be within how many mmHg of the observer's reading?

• A. 2 mmHg
• B. 4 mmHg
• C. 6 mmHg
• D. 8 mmHg

Answer: (B)

Reliable blood pressure measurement relies on a small, acceptable variation between readings. The standard tolerance is four millimeters of mercury. This margin accounts for normal differences in technique, cuff placement, arm level, and how relaxed the patient is, while still ensuring readings are dependable. If a measurement differs from another observer’s reading or a repeated check by more than four mmHg, you should reassess technique, confirm proper cuff size and arm position, have the patient rest, and repeat the measurement. A difference of two mmHg would be stricter than needed in practice, while differences of six or eight mmHg indicate poor agreement and indicate measurement error.