Measurement of physical properties on ratio scales has always been a highly desirable achievement, since these scales can contain the characteristics of order, distance, and origin while retaining maximal correspondence with the number system. Methods for constructing ratio scales of sensation have been used extensively in the past 35 years. However, as far back as 1888, Merkel was interested in finding the stimulus that doubled sensation. Merkel had observers adjust a variable stimulus so that its sensation was twice as great as the sensation produced by a fixed stimulus. A similar procedure used by Fullerton and Cattell (1892) required observers to adjust a stimulus to produce a sensation that was some fraction or multiple of the sensation produced by a standard stimulus. These procedures result in ratio scales of sensation when the ratio of one sensation magnitude to another can be specified. It was not until the 1930s, when acoustical engineers became concerned with the problem of numerically specifying psychological loudness, that psychologists became interested in ratio measurements of sensation.