The Ups and Downs of Making Elevators Go

You press a button and wait for your elevator. How long before you get impatient and agitated?

Theresa Christy, a mathematician who works at Otis Elevator, says 20 seconds. She's spent 25 years developing the math that makes elevators run as perfectly as possible. “Traditionally, the wait time is the most important factor,” she says. “The thing people hate the most is waiting.” Yet, “sometimes what is good for the individual person isn't good for the rest.”

The Ups and Downs of Making Elevators Go:

The challenges she deals with depend on the place. At a hotel in the holy city of Mecca in Saudi Arabia, she has to make sure that the elevators can clear a building quickly enough to get most people out five times a day for prayer.

In Japan, riders immediately want to know which car will serve them—indicated by a light and the sound of a gong—even if the elevator won't arrive for 30 seconds. That way, people can line up in front of the correct elevator.

Japan also boasts, in Ms. Christy's opinion, the smoothest, best-riding elevators. “When you get into an elevator there, you sometimes think you are ‘stuck' in the elevator because the motion is so smooth and quiet,” she says. But that service comes with extra costs and slower speeds.