Faria Beede Instruments Dress White 4" Speedometer - 80MPH Mechanical. 375" (85mm) Electronic speedometers operate by capturing pulses produced by a sensor. the pulses are then electronically converted to a speed reading very much like a tachometer converts ignition pulses to RPM. Pitot tube type speedometers operate by pressure from the water being forced into the pitot tube. This pressure is then transmitted through flexible tubing to the bourdon tube movement inside the speedometer head where it is converted into a speed reading by the movement mechanism. Benefits: Wide range of speeds Rugged Reliable construction Features of Faria Beede Instruments Dress White 4" Speedometer Stylish blue and white graphics Black aluminum bezel with burnished edge Flat glass lens Perimeter-lighted black dial American and metric scales and icons Package Contents: Faria Beede Instruments Dress White 4" Speedometer Faria Beede Instruments 33113: Dress White 4" Speedometer - 80MPH Mechanical