The Core 77 website has this gallery on this amusing device from 1920, the Plus Fours Routefinder, a gizmo which you wore like a watch that provided "user-advanceable mapping information at a glance" -- in other words, step-by-step instructions on getting from point A to point B.

The central design difficulties are obvious: A separate scroll was required for each point-to-point trip, which allowed no deviation. It was also unidirectional, meaning you'd have to load a new scroll for the return journey.

The device was on display as part of the British Library's "Weird and Wonderful Inventions and Gadgets" exhibition several years ago. The Mail Online theorized that the device never saw mass uptake not because of its flaws, but because it was invented too early; that there were reportedly not enough motorists in the 1920s to support mass manufacture. I'm not sure if I buy that -- you'd think that if the device had merit, one patient businessperson or another would've trotted it back out as the number of motorists rose.