A single (pilot side) Rain-Pruf wing tank gauge reports fuel level in BOTH wing tanks unless the crossover pipe is blocked.
My plane came with one in each wing tank. It does NOT cause a 2 MPH reduction in airspeed. A GPS can easily confirm that. By taking both wing tank guages off, I gained 2 miles per hour over 5000 miles, confirmed by the GPS (I also gained 5 mph by taking off the landing lights on the wheel struts covers) measured the same way.
