Tides

It is easy peasy to forecast the times and heights of the tides at any location in the world using computers. Online applications such as the UK's Admiralty EasyTide make this a click away.

But it wasn't always so easy ...

Originally, it had to be done by compex manual mathematics but then William Thomson,, later Lord Kelvin (i.e. of the temperature unit), built a mechanical tide calculator in 1872.

This was crucial to the planning of D-Day, the Allied invasion of continental Europe in June 1944. The man in the photo above is Arthur Doodson of the Liverpool Tidal Institute who led the planning team. This article in Physics Today explains.

This takes me back to pre-calculator schooldays of slide-rules and Log Tables ...

Thanks to boingboing.