Some of those old and often strange measures are still used today. Even now horse's heights are measured in 'hands'. Try it and see how close to a yard your reach is. Do the same as when you measure a yard but turn your head to the side. This extends the length by the distance between your nose and your ear.
Artists make use of what they know about the sizes of parts of the body.
Knowing that helps you measure the length of things or even the circumference of a tree. It also helps artists make sure they don't draw a person with arms that are too short or too long. Other pieces of information that help artists with proportion is knowing that the length of your hand is about the length of your face from chin to forehead. The length of your ears is about the same size as the space between your eyes and your mouth. Well, it seems as though we have very proportional bodies.