I bought an RCM-7000 guage on ebay for $50.00 with a measurement range of 4 to 30 GPM. 

 

A Google search for RCM-7000 only found a "coverslipping machine" whatever that is? So what sort of flow gauge is it that you've got there?

 

 

 I ended up buying two mechanical gauges from McMaster Carr.  One is 1-4.5 gpm, and the other is 5-30 gpm (the highest in that type of gauge).  Each was $59.  
 Rusty

  Same Question? Whacha got? Can either of these be used in flight or is it just for ground tests? Are these an orifice type? (square root extraction of DP). If so then they will add a little restriction, but this is where that pressure recovery and permanent pressure loss comes into play.

The best, most accurate and least restrictive way to measure is using a magnetic flowtube, which I used in my initial testing. Unfortunately these are unsuitable for in-flight use due to weight, size, $$$$$$$$$$$, and power requirements.

The Signet flowmeter that I used was $543 CAD. At least that's what my uuhh... "supplier" had paid for it. (obsolete stock)

Todd Bartrim