Roots flow meters consist primarily of a housing, a pair of conjugate rotors, and a counting mechanism; driven by the pressure differential (P₁–P₂) across the inlet and outlet, the rotors—maintained in precise alignment by precision-calibrated timing gears—rotate without contact while maintaining optimal clearances between each other, the housing, and end plates, achieving continuous sealing; each rotor revolution displaces four times the metering chamber’s effective volume, and the rotation count is transmitted via a magnetically sealed coupling and reduction gear to a mechanical or electronic totalizer that displays the cumulative gas volume.