I often wonder who “invented” the idea that prime number Curtas are such special collectibles? Does this special area of interest have a history? Who could give me some background information? I am a collector of calculating machines (to document the history of mechanical computing) but I never came across the idea to give prime serial numbers a special focus except for Curtas. Furthermore I wonder if for a Curta type II the whole six digit number has to be considered for a prime number analysis or if the actual production number is the relevant integer, i.e. omitting the highest digit “5” which is the type II indication? Thank you for an answer.

For a prime # Curta you have to consider the whole 6 digit serial # like you see in this ebay auction of a rare twin prime Curta II:

http://cgi.ebay.de/very-rare-CURTA-II-Calculator-with-TWIN-PRIME-SERIAL_W0QQitemZ250221528135QQihZ015QQcategoryZ414QQssPageNameZWDVWQQrdZ1QQcmdZViewItem