Just part of The Thing.

That’s not true. LeBay “helled” it.

What?

Because of the demon?

The odometer running backward in Christine had several levels of symbolism. It reflected an undoing of time which manifested in damage to the car being undone. The car was a creature that made the owner revert back to the “better” times of the 1950’s, and the odometer and the radio which only played 50’s hits was a reflection of that.

Agree with Seawulf. Christine was slowly making her way back to her beginning…whether this was due to longing for the past or perhaps it was her evil lifespan- when she reached zero, her time ended- we don’t know. Perhaps the entity which inhabited Christine had a finite amount of time to wreak havoc, and the speedo was the equivalent of the witch’s hourglass.

Thanks to a Cat D9, we will never know. :)