means Scales are either the flattened protective plates covering fish and reptiles, a device for weighing things by balancing or measuring weight, or an ordered sequence of musical notes ascending or descending in pitch.

from Two different roots got tangled here. The fish-and-reptile 'scale' comes through Old French 'escale' (a husk or shell) from a Germanic root meaning to split or peel off — a cousin of 'shell' and 'shale.' The weighing 'scale' is separate, borrowed from Old Norse 'skál' meaning a bowl or drinking cup, because the earliest balances were paired bowls hung from a beam. The musical 'scale' is yet another path: from Latin 'scala,' a ladder or staircase (think 'escalator'), since notes climb step by step. Same English spelling, three unrelated journeys.