I suggest "An Illustrated Guide To AIR METERS identification and price guide" by JACK SIM. And if you don't already have the gas pump bible, get that too.....GREAT books, he put alot of time and research into them.
Your air meter is very nice, but reminds me of a day I had skidding logs. As I was going up and down the same trail, I noticed the small green trees I was running over were becoming blacker and blacker. I thought, huh, is that motor oil or hydraulic oil? I thought it must be hydraulic because my oil pressure gauge still read 40 psi. As I finished the day, I kept close watch on my gauges, still at 40 psi but in the back of my mind I knew hydraulic oil wasn't black. The next morning, I check the oil like always and the engine oil was way low, I mean almost empty. I hopped up on the seat and I noticed the gauge still read 40 psi, WITH THE ENGINE OFF! son of a ..... fortunately, no damage.