A flow measuring system , 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 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 (C) in a first direction (E) toward the sensor, the non-normally reflecting portion adapted to reflect the incident beam (C) in a second direction (F), the second direction (F) being non-parallel to the first direction (E) such that the incident beam (C) 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 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 (C) in the second direction (F). 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 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 (C) in a first direction (E) toward the sensor, the non-normally reflecting portion adapted to reflect the incident beam (C) in a second direction (F), the second direction (F) being non-parallel to the first direction (E) such that the incident beam (C) 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 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 (C) in the second direction (F). <EOS>