The price of fuel has renewed my interest in fuel flow gauges. The Standard Horizon/Navman 2" units accurately display g.p.h., fuel used, and fuel remaining. When hull speed is available a little math quickly reveals your m.p.g.. I see that Navman now also offers a unit(3100) that interfaces with your G.P.S. via N.M.E.A.0183. This provides continuous flow rate data(mpg) as well as distance traveled and projected range in miles or hours. It too uses a 2" hole but the display is 4.4" square. I'm trying to decide if these features are worth the extra $100.00. After all, once I've determined my flow rate throughout the R.P.M. range I'll know what the most efficient engine speed is. I would appreciate the thoughts of fellow C-Brats before I decide which way to go. Pete