Deciding which type and brand of this device can be daunting.  When going through this process of choosing flowmeters, it is essential that you understand the scope of the job you want the device to do.  In addition, keep in mind the skill level of the plant personnel who will be using it on a regular basis.  If you purchase a meter that is wonderful but too complicated, you might find that you receive inaccurate results.  Of course, it also helps a great deal to understand the fluid you want to measure, including its pressure, temperature, allowable pressure drop, density (or specific gravity), conductivity, viscosity (Newtonian or not?) and vapor pressure at maximum operating temperature.