SIERRA Premier Pro Series GPS Speedometerprovides accurate speed over ground readings and heading information all in one attractive package. Includes LCD heading display to show course over ground. Use a GPS antenna (sold separately) or connect to an existing NMEA 0183 GPS device with the included connectors. Features: Speed accuracy of +/- 1 mph (once moving) Heading accuracy of +/- 1 degree (once moving) Ideal for slow speed applications like pontoon boats and high speed performance boats where pitot tubes do not perform well Gauge range: 0-120 mph