Originally, 'shaku' (in pinyin, 'shao') was a small cup with a long handle attached to its rim, and this cup seen in ancient China was for scooping up alcohol, and its capacity became the volume unit called shaku.
「勺」は元々、古代中国における、小さなコップの口縁に長い柄のついた酒をくむ用器のことであり、その容積が勺という単位となった。