A blank gauge is calibrated to read both positive and negative pressure.

• A. Barometer
• B. Compound
• C. Differential
• D. Vacuum

Answer: (B)

Measuring both positive and negative pressure requires a gauge that can read above and below atmospheric pressure. A compound gauge is designed for this purpose, using dual sensing elements or a setup that shows positive pressure on one side of the dial and vacuum on the other, with zero at atmospheric pressure. This lets you read pressures that are either higher than ambient or lower (vacuum) than ambient.

A barometer only measures atmospheric pressure, not positive readings. A differential gauge indicates the difference between two pressures but doesn’t provide an absolute reading relative to atmospheric pressure. A vacuum gauge reads only negative pressure relative to ambient and can’t show positive pressure. Therefore, the gauge calibrated to read both positive and negative pressure is the compound gauge.