The anchor said he later watched the tape of his election-night performance to check: “My hands weren’t shaking,” he said.

In his years with the map, Mr. King, 55, has developed a few rules of thumb.

First, use the appropriate finger. There was the time he pointed out a precinct with the digit between pointer and ring. “I was flipping the country the bird,” he recalled. “So you learn.”

Mr. King is left-handed, but he has trained his right hand to take care of the heavy-duty scrolling and zooming. And if he has to turn his body away from the camera, he makes sure to say “excuse me” to viewers.

“I think it’s weird on television, if you’re turning your back on somebody,” he said.

Mr. King says he works out on Election Day mornings, and he is careful to stretch his hands and wrists ahead of showtime. Washing his hands is also important, to avoid smudging the screen’s surface. How about a manicure? “I clip my own nails,” Mr. King said. “I’m a kid from Dorchester, Mass. I don’t think I’ll ever get a manicure.”

The 2018 map, he said, has sharper colors and more computing power than previous versions. “Think about your phone 10 years ago and your phone today,” he said.

The Magic Wall technology was designed for military use, in situation rooms of the C.I.A., not CNN, variety. A producer spotted it at a trade show and decided the network could take advantage.

During breaks, Mr. King retreats to a hidden nook near the map for water and espresso. “Wolf keeps a flask of whiskey,” Mr. King joked, referring to his CNN colleague Wolf Blitzer. “He’s actually a robot. We keep that from the world.”