The old way of processing credit cards involved manual imprinting of the card onto a paper sales slip using a mechanical device called an imprinter. The merchant would fill out the necessary details on the sales slip, including the customer's name, card number, and transaction amount. The customer would then sign the slip as a form of authorization. At the end of the day, the merchant would batch-process the sales slips and submit them to the credit card company for authorization and settlement.