I've never considered putting one in my own vehicle, since scheduling maintenance by mileage or calendar time seems adequate to me.

Some military trucks have hour meters in addition to odometers, and they idle A LOT. I've seen some where the mileage divided by the hours works out to an average speed of about 3 mph.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.