Autometer Gauge Speedometer 3-3/8in 80MPH Mechanical Marine Carbon FiberAn Easy And Affordable Solution To Determine Your Speed Over The Water. Autometers Pitot Tube Style Speedometers Are Essentially A Precisely Calibrated Pressure Gauge. Speed Is Determined By Measuring The Water Pressure Entering The Pitot Tube That Extends Into The Water In The Path Of The Boat. This Is Translated Into Miles Per Hour To Give You An Accurate And Reliable Indication Of Your Speed. This Is A Time Tested Design That Is A Great Option For