The pupillary distance (PD) measurement is a requirement for people who want to purchase eyeglasses. Here, find out how to measure your PD using a mirror and a ruler. Share on Pinterest Some eyewear ...

iOS: Sometimes you need to get a quick measurement of something and you probably don’t carry a ruler around, but of course, there’s an app for that. VisualRuler gives you a decent estimate of an ...

The cosmic distance ladder is the world’s longest ruler, built to measure the universe. Since the time of the ancient Greeks, scientists have been constructing a cosmic measuring tape to measure the ...