Turbine flowmeters typically have a 10:1 turdown accuracy. With good bearings and more precise machining, 50:1 is reasonably attainable. A high – priced RF pickoff can eliminate magnetic reluctance on the turbine, and get you to 100:1. Factors such as viscosity, density, and air entrainment (for liquids) also effect accuracy. Only a positive – displacement flowmeter is truly accurate, but with that comes pressure drop and cost issues. $130 is pretty reasonable for a turbine and conditioning circuitry.
All I want this thing to do is tell me how much beer is left in my keg. Inspired by the Sparkfun Tweeting Kegerator? You bet!