Use simpler wording: He got a patent on his machine and started a company the next year to make them, but it was not popular and the company, which became the National Cash Register Company in 1884, was sold to John H. Patterson.
In 1884 Eckert sold the company to John H. Patterson, who renamed the company the National Cash Register Company and improved the cash register by adding a paper roll to record sales transactions, thereby creating the journal for internal bookkeeping purposes, and the receipt for external bookkeeping purposes.