Card imprinter
The mechanical sled that pressed a card's raised digits through a carbon slip, and the reason payment cards carried embossed numbers for so long.
The merchant laid the card in a bed, put a carbon-backed slip on top and racked a roller across and back. The sound gave it the nickname "zip-zap machine"; anyone who caught their fingers called it a "knuckle buster". The customer signed, one copy went to them, one stayed with the shop and one was physically sent to the acquirer. Below the floor limit no phone call was needed, and the only defence against stolen cards was a printed list of bad numbers.
The carbon paper was a security hole in its own right: the discarded sheet carried the full card number in mirror writing and was a favourite source for fraudsters. Imprinters lingered for years as a backup during power cuts. Once they were finally gone, embossing had no purpose either, and a growing share of cards now ship flat, with the number printed on the back or only in the app.