Electromagnetic 2 Speed Log Display Data Box Electromagnetic LogThe Clipper electromagnetic speed log measures the boat&';s speed through the water without moving parts.Robust and accurate, the sensor generates an alternating magnetic field below the boat and measures the resulting electric field produced by the boat moving through the water. It is designed for installation into most types of GRP hulls.With excellent linearity and a resolution of 0.1 Knot, over the range of 0.2 to 40 Knots, the log sensor sends signals to a control box which then converts the sensor signal to boat speed, trip, and total distance. This data is transmitted in NMEA 0183 format to a Clipper EM Log display unit.*NOTE - NOT SUITABLE FOR METAL HULLSSpecifications: Clipper EM Log display 110 x 110mm industry standard square case NMEA 0183 input Speed in Knots Trip and Total logs in nautical miles Multi-level display backlighting This product may not be returned to the original point of purchase. Please contact the manufacturer directly with any issues or concerns.