1920s Wristwatch-Style Routefinder

A display of unusual gadgets and inventions at the British Library includes a wrist-based routefinder that used miniature scrolling maps to indicate your destination. The Daily Mail and Ananova (which have pictures) call it the 1920s-era equivalent of satellite-based navigation, but I don’t think that’s the right metaphor — I think it’s more like TripTiks in a wristwatch. Via MapHist (thanks, Tony).