The diagnostics on Bell's early electronic switches would actually light a green light on each good printed circuit board, and light a red light on each failed printed circuit board.
Dijagnoza na Belovim ranijim elektronskim prekidačima, zapravo bi upalila zeleno svetlo na svakoj dobro odštampanoj kolnoj ploči, a crveno svetlo na svakoj neuspelo odštampanoj kolnoj ploči.