Scott,
You have received a number of answers to your query, so I will just jot down a few lines. If you need any further information let me know.
1) Various methods are available for proving a gas system from other inline meters (ultrasonic, turbine, orifice plate, bell prover etc). All these...
Dependant on the accuracy (uncertainty) required turbine, orifice plate, coriolis, ultrasonic meters could be used. As always highly accurate flow measurement works out expensive. If you let me know what accuracy you are trying to acheive, I can give you some further information.
A good question it all depends on the product you are trying to measure (single/dual phase, gas, liquid, slurry etc), also the overall accuracy (uncertainty) you are trying to achieve. International Standards covering the measurement of flow to high accuracy are again quite numerous, ISO 5167...
