Twitter co-founder Jack Dorsey’s tech start-up Square — known for the white plastic attachments that transform iPhones into credit card readers — is offering small business owners access to more detailed sales trends.

Square announced on Thursday that it was adding a new analytics feature to its iPad app, Square Register, which lets business owners charge customers for particular items in their inventories.

For instance, owners can track which items sell fastest and when they change hands — if hot drinks are more popular during a certain hour, owners might know when to prepare them. Sellers can also track how many customers are new, how many are returning, who are the most frequent, and average customer spend, among other metrics.

Dorsey hinted in an interview with the Washington Post last year that the company planned to grow its data services.

“The original focus was around running your business, specifically participating in commerce,” he said then, describing how Square’s plastic credit-card reader was designed to help small business owners to process payments without renting a register.

But he added, “more and more it’s about growing your business, and growing your business through analytics.”

The new service could be an effort to distinguish Square from competitors. Last week Amazon announced its own credit-card reader attachment for smartphones and tablets, and the mobile payment industry is packed with players such as PayPal and Intuit vying for the small business owners’ market.

They all are presenting themselves as cheaper alternatives to the credit card processors banks traditionally provide. Square, for instance, charges a flat 2.75 percent per credit card transaction — often banks negotiate transaction fees with small business owners. (Disclosure: Amazon’s chief executive, Jeffrey P. Bezos, owns The Washington Post.)