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. <EOS>