You might find some more information on my website -
http://petrolianacollectibles.com/Then click on the bottom of the page, you will see Air Meters, just pick one of them at a time for more air meter information.
I need to add this, this site is dormant, I cannot add/delete/or change anything on it because it is no longer supported by MS. Because of this prices and availability my have changed.
As for buying a used air meter the information I have on this page -
http://petrolianacollectibles.com/restored-pedestal.htm tells about why you should buy a air meter from me (but at the present time I don't have any to sell), but the information will help you in the purchase of a meter.
Jack Sim