GPH Range on a Northstar F-210, is about as far as you can throw it, preferably towards a trashcan.
If you have not already purchased DO NOT!!! read the reviews everywhere, THT and the internet. I bought one when I was restoring the Osprey because I thought I was going to rebuild the Johnson, wound up going Yammi, and inistalled it anyway, because I could not afford the Yamaha Fuel Management system. What garbage... their cust support will keep stonewalling you telling you, you have to calibrate it... bla bla bla... The actual advertised range I think is around 25 or 30 GPH, but mine would never read the same thing for more than a few seconds, it was all over the place, .2, 5, 10, 20, .8 etc.... My neighbor bought one for his WC Cuddy I/O and it does the same thing. Save your money. Call Marine Connection Liquidators (in this thread), have them ship you the yamaha fuel management system, its the gauge, the harness, and transducer, works great on any motor. 295.00 complete, or go with the "Flow-Scan" system, they have good reviews. I just finished hooking my FMS up last night on the yamaha, right out of the box, rock steady reading.... LOVE IT.
Marc