This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Pat no Strowger. Patentschrift Automatic Telephone Exchange de Saibo CommonsHelper Strowger PDold PDUSpatent Original upload log page de AutomaticTelephoneExchange Matthias Bock bytes no Telephone Exchange andere Version AutomaticTelephoneExchange PD da vor dem Januar verffentlicht Strowger switches