Thanks for the pics.
Have you tried putting a fluid through the OG2?
I found this description of an Oval Gear Flow Meter.
Oval Gear Flow Meters
Oval Gear flow meters are designed to function in applications that require an accurate volume dispensing of water solutions or any other liquid, including for use in brake fluid, wiper fluid and antifreeze applications.
I have found references to using OGM for gas measurement, but yours only mentions oil and water specs.
The cal sheet you posted uses water as its test medium.
So gas as in blowing through them will probably not produce a response due to its very low viscosity.