We've already seen the 1000 MPH Rolex built for the Bloodhound SSC land speed record hopeful. Now, driver Andy Green explains exactly why he needs it.
Basically, if there's a catastrophic failure of some kind and all the electronics go out, that Rolex speedo and clock/stopwatch run on their own power. They'll be what Green uses to bring the LSR vehicle to a stop. The speedo has its own GPS, even.
It's easy to make jokes about watches being redundant, but when you're looking to break 1000 mph, sometimes redundancy is exactly what you need.