I had to return a vehicle today and needed a ride home, so I engaged the services of my husband. I drove a Subaru Impreza, while he followed along in a Mercedes-Benz M-Class, both of them new vehicles.
We got onto the highway, and I set the cruise control on my car to 105 km/h. All the way out - about a half-hour trip - the speedometer never varied from that.
But he certainly did. I'd look in my rearview mirror and he'd be way off in the distance; then he'd catch up and be right on my back bumper. After a while he'd fade off again.
When we finally got to our destination, I said, "Why did you keep falling back and then speeding up?" He said, "Me? I was trying to figure out why you were doing that. I kept saying, 'Why isn't she using the cruise control'?"
It turns out both of us had our vehicles on cruise, and both of us noted that our speedometers didn't vary from what we'd set. (My cruise was indicated by the speedometer; his had an electronic readout for the speed.) This is the second time this has happened, although I don't remember which cars we were driving then. Both cars set to the same speed, and yet they vary wildly. How many cruise control systems are out there that aren't maintaining the speed we think we've set?