If you've got a car, you probably own one of those pen-sized tire-pressure gauges. It's got a funny little spherical thing on one end and a little sliding scale on the other end.

A tire pressure gauge is a relatively simple device. See more tire pressure gauge pictures.

Have you ever wondered how it measures the pressure? And why doesn't the little scale just blow out the end?

In this article, we'll figure out exactly how these pressure gauges work!