Pressure measurement Absolute Pressure: Measured relative to perfect vacuum Perfect vacuum: 0 absolute pressure Gauge Pressure: Measured relative to local atmospheric pressure If no specified, pressure reading is usually assumed to be gauge Gauge pressure is positive if higher than atmospheric pressure, and negative if lower than atmospheric pressure Negative gauge pressure is also known as suction or Ⅴ acuum pressurePressure Measurement • Absolute Pressure : Measured relative to perfect vacuum • Perfect vacuum : 0 absolute pressure • Gauge Pressure : Measured relative to local atmospheric pressure • If no specified, pressure reading is usually assumed to be gauge • Gauge pressure is positive if higher than atmospheric pressure, and negative if lower than atmospheric pressure • Negative gauge pressure is also known as suction or vacuum pressure