When using sight-size, the painting or drawing is placed next to the sitter so that both appear the same size when viewed together from a given distance. In this way, shapes and proportions, colours and values can be evaluated to scale alongside nature. First documented by Roger de Piles in 1708, sight-size is primarily a portrait practice as used by Reynolds, Raeburn, Sargent etc., but because it facilitates a direct comparison between subject and image, it is the best way to train the eye and therefore fundamental in an educational context.