For the next hour and a half, he signed 141 copies with blue Sharpie pens, fortified by a mug of coffee that a museum staff member placed in front of him. The mug, which the museum sells for $19.95, boasts in all caps: “I Finished The Power Broker.”Caro usually dislikes cracks about the book’s length. But he seemed delighted by the mug.“Did you see this?” he asked, holding up his coffee.“I’m not supposed to say this,” he said, “but I kind of like it.”

I suggest to Caro that it’s become one of those things young New Yorkers do, or at least say they do, on the path to becoming a serious adult: Get a Met membership, figure out where Film Forum is, buy (and maybe even finish) The Power Broker.

It is quite large, the letters along its spine are big and bright, and readers are required to own it in print, because Mr. Caro, who still uses a typewriter, has refused to distribute the written version in any other way.