It’s easy to take something as simple as the elevator for granted, but there are a huge number of factors involved in making the process of going up and down as smooth as possible. The Wall Street Journal interviewed Theresa Christy, a mathematician who calculates all the possible variables for making elevator rides in different locations as quick and smooth as possible. While there are plenty of mathematical problems that need to be taken into account, there are also other issues at play: average weights between nationalities can fluctuate dramatically, while different cultures across the world expect different elevator experiences.