I've been looking at different gauges to put on my bike and every speedometer I've found uses the sensor and the magnet, has anyone used these before? I'm uncertain about the setup and how accurate it is so I wanted to ask before I dish out any money on it

 

Most speedo's old and new use the same principle best explained here

Speedometer - Wikipedia, the free encyclopedia

 

A friend of mine got one from a bicycle shop and mounted it to his Yamaha. His factory one was off a bit but the one I mentioned can be programed for tire Dia. He checked it with his GPS and fiddled with the Dia. and now he says it matches the GPS.

 

that's what I like to hear, thanks man, and thanks sprock.