3.5 cun lateral to the lower border of the spinous process of the 1st lumbar vertebra (L1).
How to locate
First identify the Tuffier's line which connects the highest points of the iliac crest. The spinous process of the 4th lumber vertebra (L4) mostly falls on this line.
Then identify the 1st spinous process of the 1st lumber vertebra (L1) by counting up three.
Pigen EX-B-4 is 3.5 cun lateral to the lower border of L1.