Proximity Switch Help

[n4rsn]

I have a question.  Is the pick-up unit for a speedometer, or a tachometer, just a Proximity Switch?     If it is, is it a magnetic, capacitave, inductive, or what ever else is out there.   I know a Proximity Switch, is a whole lot cheaper than a pick-up unit, with a name on it, from an instrument company.
Thanks
Steve
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Huh

[Rick Brown]

A magnet and Hall Effect sensor are often used to sense shaft rotation.
-Rick Brown in Reno, NV