This type of meter replaced earlier models with registered acre feet (now megalitres). approx 1980. Meters on wheels have been used for approx 80 yearsMeter for attachment to dethridge wheel to measure megalitres of water. This type attached to the wheel and revolves with it. (Older type attached to the axle) This one is for a large wheel.S.R.W.S.C M.L L.M.O I.D. No-MD070942irrgation, dethridge wheel