A gas sensor apparatus, comprising: a flange; a bellows; said bellows supported by said flange; a port, said port communicating gas between a gas reservoir and said bellows urging said bellows in an expanding direction; a base plate, said base plate supported by said flange; a bellows coupling, said bellows coupling includes a pivot portion; a movable lever; said bellows residing between said flange and said bellows coupling; said bellows coupling residing between said bellows and said lever, said pivot portion of said bellows coupling engaging said movable lever displacing said lever in response to the temperature and pressure of said gas; an adjustable bias mechanism, said bias mechanism engages said lever; a bimetallic element, said bimetallic element affixed to said lever and to said base plate; an electronic distance sensor, said electronic distance sensor includes a first element affixed to said lever and movable therewith, and said sensor includes a second element affixed to said base plate; characterized in that the gas sensor apparatus further comprises an electronic microcontroller; said second element of said electronic distance sensor detecting said distance between said first element of said electronic distance sensor and said second element of said electronic distance sensor, said electronic distance sensor outputting a signal representative of said distance between said first and second elements to said microcontroller; a temperature sensor, said temperature sensor outputting a signal representative of said temperature of said bimetallic element and said gas to said electronic microcontroller; said microcontroller determining a temperature compensated pressure of said gas within said gas reservoir; and, said microcontroller determining the gas density within said gas reservoir. a flange; a bellows; said bellows supported by said flange; a port, said port communicating gas between a gas reservoir and said bellows urging said bellows in an expanding direction; a base plate, said base plate supported by said flange; a bellows coupling, said bellows coupling includes a pivot portion; a movable lever; said bellows residing between said flange and said bellows coupling; said bellows coupling residing between said bellows and said lever, said pivot portion of said bellows coupling engaging said movable lever displacing said lever in response to the temperature and pressure of said gas; an adjustable bias mechanism, said bias mechanism engages said lever; a bimetallic element, said bimetallic element affixed to said lever and to said base plate; an electronic distance sensor, said electronic distance sensor includes a first element affixed to said lever and movable therewith, and said sensor includes a second element affixed to said base plate; characterized in that the gas sensor apparatus further comprises an electronic microcontroller; said second element of said electronic distance sensor detecting said distance between said first element of said electronic distance sensor and said second element of said electronic distance sensor, said electronic distance sensor outputting a signal representative of said distance between said first and second elements to said microcontroller; a temperature sensor, said temperature sensor outputting a signal representative of said temperature of said bimetallic element and said gas to said electronic microcontroller; said microcontroller determining a temperature compensated pressure of said gas within said gas reservoir; and, said microcontroller determining the gas density within said gas reservoir.