Abstract: A mass flow meter comprising a housing including a fluid inlet and a fluid outlet. The housing defines a chamber and a rotatable member is arranged in the chamber so as to be rotatable about an axis. A momentum device is also arranged in the chamber and connected to the rotatable member via a biasing element so as to be rotatable about the axis and rotatable relative to the rotatable member. A fluid path in fluid communication with the fluid inlet and the fluid outlet is provided. The fluid path passes through both the rotatable member and the momentum device. The fluid path enters the momentum device at a radial distance r1 from the axis and exits the momentum device at a different radial distance r2 from the axis. A torque provider may be coupled to the rotatable member via a shaft or gear member.