[Cryptography] What is a "white code" cylinder?

[Dave Horsfall]

In "The Code Book" by Simon Singh (a good read, BTW) there is a reference 
to comparing the Najavo code speakers with 'his "white code" - a 
mechanical ticking cylinder thing' (the Najavo speakers won).  This sounds 
like some sort of a synchronised timing device, but I cannot find anything 
about it.

-- Dave