A flow measuring system (10,100), comprising: a housing fluidly coupled to a fluid inlet and a fluid outlet, the housing defining a passage for a flow of a fluid; a first rotating member disposed in the housing; a second rotating member disposed in the housing, the second rotating member intermeshing with the first rotating member, the first and second rotating members (114,116) adapted to rotate synchronously in response to the flow through the passage of the housing, at least one of the first rotating member and the second rotating member having a normally-reflecting portion and a non-normally reflecting portion; and a sensor operatively connected to the housing, and being optically aligned with the normally-reflecting portion, the normally-reflecting portion adapted to reflect an incident beam in a first direction toward the sensor, the non-normally reflecting portion adapted to reflect the incident beam in a second direction, the second direction being non-parallel to the first direction such that the incident beam is reflected away from the sensor, the sensor adapted to measure optical characteristics of a beam reflected by the normally-reflecting portion, and determine at least one of a rotational count indicative of a number of rotations of the first rotating member or the second rotating member, and a speed of rotation of the first rotating member or the second rotating member based on the optical characteristics of the beam reflected by the normally-reflecting portion, wherein the flow measuring system (10,100) determines characteristics of the flow based on at least one of the rotational count and the speed of rotation; and characterised in that the non-normally reflecting portion comprises a plurality of grooves, each groove adapted to reflect the incident beam in the second direction. a housing fluidly coupled to a fluid inlet and a fluid outlet, the housing defining a passage for a flow of a fluid; a first rotating member disposed in the housing; a second rotating member disposed in the housing, the second rotating member intermeshing with the first rotating member, the first and second rotating members (114,116) adapted to rotate synchronously in response to the flow through the passage of the housing, at least one of the first rotating member and the second rotating member having a normally-reflecting portion and a non-normally reflecting portion; and a sensor operatively connected to the housing, and being optically aligned with the normally-reflecting portion, the normally-reflecting portion adapted to reflect an incident beam in a first direction toward the sensor, the non-normally reflecting portion adapted to reflect the incident beam in a second direction, the second direction being non-parallel to the first direction such that the incident beam is reflected away from the sensor, the sensor adapted to measure optical characteristics of a beam reflected by the normally-reflecting portion, and determine at least one of a rotational count indicative of a number of rotations of the first rotating member or the second rotating member, and a speed of rotation of the first rotating member or the second rotating member based on the optical characteristics of the beam reflected by the normally-reflecting portion, wherein the flow measuring system (10,100) determines characteristics of the flow based on at least one of the rotational count and the speed of rotation; and characterised in that the non-normally reflecting portion comprises a plurality of grooves, each groove adapted to reflect the incident beam in the second direction.