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A sphygmomanometer that allows the blood pressure to be taken without the observer's knowing where zero pressure is on the device. After the pressure is obtained, the mercury comes to rest at a point. The observed pressure is then corrected by subtracting the at-rest value on the device from the pressure obtained. Although this device was developed to prevent subjective bias in determining blood pressure, it is not necessarily effective in achieving this goal.
See also: sphygmomanometer