Music transposer
A music transposer is a software program, physical or electronic device for the transposition of musical notes and/or chords from one note/key to another. It simply consists of two identical scales which can be moved in relation to each other to give the required result. Until 1994 transposers consisted of sliding three transparencies alongside each other. In November 1994 the circular transposer was invented by Terence Tranter, a British resident in Australia. This device consisted of two circular discs one with a larger diameter. Along the edge of both discs was printed the chromatic musical scale. the  smaller disc was pivoted centrally allowing it to rotate in relation to the other, each scale being visible. By aligning the known note of a scale with the note of the required scale it is possible to read all the notes in relation to each other.