Bone-length measurement means to use the major bones in the human body as signifiers to measure the length and size of each region and change into proportional　units as  the  criteria  for  locating  acupoints  (see Table 1-4 and Fig. 1).
Since the acupoints on the chest and side of the chest are mainly located in the costal interstices or parallel to the costal interstices, the costal interstices are used as signifiers to locate these acupoints.