Today, Panasonic Automotive showed off its 4K-resolution AR HUD, which covers a much larger section of the windshield and mixes two-dimensional information such as vehicle speed, speed limit, and fuel range in the near-field view with three-dimensional overlays of navigation directions in the far-field view, which appear to be cast spatially onto the road ahead.
That's the premise of the book How to Invent Everything: A Survival Guide for the Stranded Time Traveler, by Ryan North.Without getting into the nitty-gritty details, it gives you the general idea of how things like an electric motor or wifi work. If you can build a radio transmitter, you won't need a clock.