TwinScan™ Instruments embody a new concep t in twin engine analog instrumentation which sets the ultimate standard f or easy readability in the least possible space. Each individual instrument c ontains port and starboard meters which reference to each other. TwinScan ins truments reduce the panel space required by 50% leaving more room for other electronics. TwinScan Fuel Flowmeters and Tachometers are sold separately. Features Tachometer / MPG / Synch Indicator uses an NMEA 01 83 speed signal from a GPS or Loran, and a fuel flow signal from a TwinScan ™ GPH instrument to digitally display Fuel Efficiency (nMPG) or the RPM differen ce between port and starboard engines. Requires 1 SPST toggle panel switch for r eading nMPG or engine synch. See Accessories page for recommended toggle switch (TG40020) for this feature. Microprocessor electronics for high performance fe atures like electronic dampening, linear dial scales, superior accuracy u naffected by ground voltage shifts. Patented, magnetically shielded, precision, miniat ure air-core meter movement with state-of-the-art engineering features. Corrosion free stainless steel bezel (black, white or polished) and molded acetal cases which fit standard 3-3/8" diamet er holes. Reverse polarity and load dump protection exceedin g SAE J1810 standards. Dial faces: Black on White, or White/Red on Black. U.S & Metric Scales.