4" Speedometer 50 Knot - Chesapeake White - Stainless Steel BezelElectronic TypeElectronic 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 TypePitot 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.Features:Wide range of speedsRugged, Reliable constructionMechanical, Electronic, Pressure (Pitot) types available4" - Hole size: 3.375" (85mm)Chesapeake WhiteStainless Steel Bezel50 Knot