In Traditional Chinese medicine (TCM) we use proportional measurements to locate acupuncture points on the body. This measurement system is known as cun. 

Whole regions of the body are divided up into equal parts. For example the outside of the thigh is divided up into 19 equal parts while the outside of the calf is divided into 16 equal parts. Each part is 1 cun measure.

A quick way of determining 1 cun is by using the middle phalanx of your middle finger or the width of your thumb.

Because we all come in different shapes and sizes this means that my cun is different from yours. 

image: A Manual of Acupuncture, Peter Deadman & Mazin Al-Khafaji with Kevin Baker