In my original post, I did not use the abbreviation 'BB', because I knew it would be unfamiliar to many. The Black Box was what Carrera called their digital powerbase for it's first 3 generations. And while it isn't a very happy one, you did get an answer to your question about the port on the back of the 30355 lap counter: it has no use to the end user. This has been true for 10 years now.I´m sorry, but what is a BB? In fact it´s ashame that I can´t find an answer somewhere.