 As the three genera simply represent ranges of possible intervals within the tetrachord, various "shades" ("chroai") with specific tunings were specified.Once the genus and shade of tetrachord are specified, their arrangement can produce three main types of scales, depending on which note of the tetrachord is taken as the first note of the scale.The tetrachords themselves remain independent of the scales that they produce, and were never named after these scales by Greek theorists.