The answer man adjusted his headset, settled into his office chair and faced the next caller’s question.

“Hello, Ask N.Y.P.L.,” said the library researcher, Matthew J. Boylan, 54.

It was an official at the United States Holocaust Museum in Washington asking about Jews in early-20th-century Thessalonika.

“Well, Thessalonika was part of the Ottoman Empire,” said Mr. Boylan, who steered the caller to a set of digitized oral histories in the library’s Dorot Jewish Division.

The next caller needed a certain biology textbook. Another wanted help finding rare films of drama productions. Another was calling for her nephew.