Flow meters are used to measure the rate of flow of liquids or gases, just like electric meters measure the amount of electricity consumed. However, unlike electric meters, which are either electro-mechanical or electronic meters, there are just too many variants in flow-meters, all with different concepts on how the flow of fluid is measured, with some even customized to measure special fluids. A new generation of electronic flow meters provide better control and accuracy of fluid measurement, however still leave several choices on how fluid is measured. Part I of this series covers basic flow meter fundamentals including types of flow meters and the main considerations and challenges in selecting a flow meter.