What is a cun?

There are a variety of basic ways to find a cun depending on where you are planning to find points (thumb, finger, your four fingers together from knuckle to knuckle, distances between body landmarks, distances between "obvious" points - such as those on the wrist crease or in a space created by a tendon, etc.). Again, as stated above, "the cun is a relative measurement tool - relative both to the individual you are finding points on and relative to what part of the body you are finding those points." You would never use your own or someone elses "cun" to find points on another person. Your statement about the cun being a "dubious" measurement because of the differences in peoples thumbs clearly misses this point.

In clinical reality, as I've also stated, practitioners are trained to "know" where the points are and very few practitioners actually measure out the point locations after they have some clinical experience. The cun is in some ways merely a training device. It is, however, much more accurate than a concrete statement which seems easier to grasp with the western mind. You could, for example, say a point is between tendon x and tendon y 5cm from the wrist crease. However, on a person with a short forearm this would be inaccurate as well as on a person with a particularly long forearm. Hence the cun - a relative measurement tool - is the only "accurate" way to consistiently measure for acupuncture points.

To help, the cun measurements that are most useful for each meridian are listed in that meridians "General" information section. The Lung Meridian, for example, relies on the following measurements:

Sternum --> Coracoid Process = 6 cun
Sternum --> Acromion Process = 8 cun
Axillary Fold --> Cubital Crease = 9 cun
Cubital Crease --> Wrist Crease = 12 cun

Note there is no mention of using the thumb or the finger to measure for points.

The Spleen Meridian uses the following measurements:

Lower border of medial condyle of tibia (SP 9) --> tip of medial malleolus = 13 cun
Upper border of symphysis pubis --> medial epicondyle of femur = 18 cun
Sternal costal angle --> CV 8 = 8 cun
Anterior midline --> Spleen line on abdomen = 4 cun
Anterior midline --> Spleen line on chest = 6 cun
Clavicular lateral measurement = 8 cun
Axillary fold --> 11th rib = 12 cun
Upper border of symphysis pubis --> umbilicus CV 8 = 5 cun

I hope this helps to make the dynamic nature of the "cun" more clear.

Yin Yang House Acupuncture & Energy Healing Clinic

BUT i READ THIS FROM SOMEWHERE THAT IS ACTUALLY THE WIDTH OF THE THUMB.i AM ALSO DUBIOUS ABOUT THIS MEASUREMENT AS EACH PERSON'S THUMB IS DIFFERENT FROM DIFFERENT INDIVIDUALS.cAN SOMEONE COME OUT TO CLARIFY THIS POINT.
tHKS

Yes, there are a few devices for sale that are used as learning aids and in schools students often take a long piece of elastic band and mark measurements on it. The band can then be stretched to accommodate individual cun variations on different people and on different parts of the body.