Base data: length.
There are various stories such as it is the length from the bottom of the palm to the tip of the middle finger
Based on hand size but not an exact measurement
Uniquely Japanese units that came before those from China, such as the shaku, make an appearance in Kojiki (Records of Ancient Matters) and Nihon Shoki (Chronicles of Japan). One of those, the ata unit, is based on the size of the hand. Unfortunately, we do not know the exact length. The “yata” in “yata-garasu”, the sacred crow who guided Emperor Jinmu refers to the length of 8 ata.
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