You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Fresno,_California

Context:
In September 1958, Bank of America launched a new product called BankAmericard in Fresno. After a troubled gestation during which its creator resigned, BankAmericard went on to become the first successful credit card; that is, a financial instrument that was usable across a large number of merchants and also allowed cardholders to revolve a balance (earlier financial products could do one or the other but not both). In 1976, BankAmericard was renamed and spun off into a separate company known today as Visa Inc.

Question:
What did the BankAmericard allow customers do to that they couldn't do with previous financial instruments?

to revolve a balance