What is the side slot on the HP 41CX for?

[brouhaha]

(09-07-2014 12:38 AM)Namir Wrote:  The first HP-41C calculators came with a rechargeable battery pack.

Actually the first ones sold came with the N-cell holder, and had spring-loaded contacts in that side hole for a power adapter that never shipped.

It wasn't until later that the 82120A rechargeable battery pack was introduced. Fortunately (or perhaps through good planning) the hole was suitable for the 82059 and related chargers, which had been used for some earlier HP calculators, such as the 97 and 19C.