'true-to-scale' originates from English, formed as a compound of 'true' and 'scale', where 'true' ultimately comes from Old English 'trēowe' meaning 'faithful/true' and 'scale' derives via Latin 'scala' meaning 'ladder' or 'steps' (later extended to a graduated series or measure).

'true' developed in Old English as 'trēowe' meaning faithful or accurate, while 'scale' moved from Latin 'scala' through Old French into Middle English with senses including 'ladder' and 'a graduated series' and eventually 'scale' as a measuring/ratio concept; the compound 'true to scale' arose in Modern English to describe correctness of proportion.

Initially, 'true' meant 'faithful' and 'scale' originally referred to ladders/steps; over time 'scale' acquired the sense of 'graduated measure', and together the compound came to mean 'accurate in proportion' as used today.