yea, ball valves are worthless
all of the flow meters are of the DC pulsed mag type
have Sparling, Foxboro, Yokogawa, and Danfoss
a typical accuracy description is below
at 0.3gpm with a 1/4" flowtube I'm at ~1.5%, maxes at just under 4gpm
note the oscillations described, several hundred 1~ readings should be averaged