On the line joining the olecranon and Jianliao TB-14, midway between Qinglengyuan TB-11 and Naohui TB-13, 5 cun proximal to the olecranon.
It is just one the lower end of bulge of the lateral head of triceps brachii when the forearm is in pronation.
How to locate
Abduct the arm and locate two depressions below the acromion. Locate Jianliao TB-14 at the posterior depression, below the posterior aspect of the lateral extremity of the acromion.
Then locate Tianjing TB-10 in a depression 1 cun above the olecranon. Draw an imaginary line between TB-14 and the olecranon. Measure TB-12 on this line and 4 cun above TB-10.
Or use the 'spreading hand technique': Place the little fingers on TB-14 and TB-10 respectively and determine the midpoint of this distance with the thumbs. From the midpoint, measure 1 cun in a distal direction and locate TB-12 there.