Type in a message, and this website will translate it into the Popham flag code in use by the Royal Navy (1806 version). For example, the title of my blog looks like this:
|163 756 85
The signal is read from left to right and top to bottom. The red/white flag is the telegraphic flag that says the code book is being used. The diagonal blue/yellow flag shows that the signal is finished. That graphic may turn up elsewhere on this blog later. If you're interested in the Popham code, the 1803 book is available on Google Books. Just search for "Popham signal code" and it should be the first result.