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Symbol indicating that a gas volume has been expressed as if it were saturated with water vapor at the ambient temperature and barometric pressure; the condition of an expired gas equilibrated in a spirometer. ... (05 Mar 2000) ... 
ambient temperature and pressure, saturated; denoting a volume of gas saturated with water vapor at ambient temperature and barometric pressure.
AppleTalk Printing Services [Macintosh]
Type: Symbol Definitions: 1. Symbol indicating that a gas volume has been expressed as if it were saturated with water vapor at the ambient temperature and barometric pressure; the condition of an expired gas equilibrated in a spirometer.