Flow meter (Flo-Gage) measures flow based on a pressure differential created across a built-in calibrated nozzle.   It is suitable for measuring water, oil, and most other low viscosity liquids which do not deposit out and which are compatible with the materials of construction.  It is also suitable for measuring compressed air, oxygen, carbon dioxide and many other non-toxic compressed gases.  The Flo-Gage can be fitted with a transmitter with current or frequency outputs for remote indication or totalization, or with reed switch contacts for signaling high or low flows.