The cun is a measurement relative to the patients body that is used to find acupuncture points. Generally speaking one cun is equal to the space between the distal interphalangeal joint and the proximal interphalangeal joint on the middle finger. However, this cun can only be used on certain parts of the body when finding acupuncture points - on other points you use other relative landmarks. For example, the space from nipple to nipple is 8 cun and this 8 cun can be used to find points on the chest - the space from the center of the patella to the lateral malleolus is 16 cun and this 16 cun can be used to find points on the legs, etc. These cun landmark relationships are found within the "General" link for each meridian under the "Measurements Needed" section. For example - Stomach Meridian General Information.