World's Earliest SatNav

I love my satellite navigation system but this device was an idea apparently far ahead of it's time (and satellites):

Satellite navigation (SatNav) is a lot older than previously thought. In fact, it’s even decades older than man-made satellites themselves. This fantastic contraption, called the ‘Routefinder’, showed 1920s drivers in the UK the roads they were travelling down, gave them the mileage covered and told them to stop when they came at journey’s end.

The technology - a curious cross between the space age and the stone age - consisted of a little map scroll inside a watch, to be ’scrolled’ (hence the word) as the driver moved along on the map. A multitude of scrolls could be fitted in the watch to suit the particular trip the driver fancied taking.

I question the safety of constantly looking at your wrist for directions while driving but I suppose the dearth of cars at the time made the chances of a collision much less likely than today.