1. Field of the Invention
The present invention relates to a transposition rule for musical theory for the visual indication of the sequence of notes of musical scales and/or chords in the various keys of a tone system. The transposition rule includes an elongated base member which is provided with fixed scales, wherein the scales include the notes of the tone system arranged with a uniform division, and replaceable sliding scales which are displaceably guided in the base member and are provided with the sequences of notes of the musical scale and of the chords in a division corresponding to the division of the fixed scales.
2. Description of the Related Art
A transposition rule of the above-described type is disclosed in British Patent 185 862. The transposition rule can be used as an educational aid for beginners as well as for advanced students and contributes to a better understanding of the relatively complicated spatial concept of the Western or Occidental tone culture which is based on the so-called diatonic tone system which is a 12-tone system of halftone steps. The scale based on this system includes eight tone steps, wherein the degrees from the third to the fourth tone step and from the seventh to the eighth tone step are halftone steps. The tone steps between all other degrees are whole-tone steps. Each composition which is written in a key which differs from the key of C must correspond to the sequence of whole-tone steps and halftone steps predetermined by the above-described scale system. Accordingly, the relatively complicated principle of having to fit 12 individual tones depending on the selected key into a system of tones with different spacings (musical scale) is not only difficult for beginners, but also for teachers who have to impart these frequently difficult relationships to students. This is also true with respect to active musicians who have to carry out complex mental efforts when constructing scales and chords, so that mistakes can frequently not be avoided. The above-described transposition rule can be of help in this connection.
Analogous to a slide rule, the known transposition rule has a tongue-like slide member which can be pulled out and reinserted or which can be exchanged against slide members with different scales. The base member of this transposition rule is provided on its upper side with fixed scales and it includes a dovetail-type guide means into which the tongue-shaped slide member can be inserted. However, as is the case in a slide rule, it is necessary to pull out the slide member over its entire length from the dovetail-type guide means at the end of the base member and, when reinserting the slide member or inserting another slide member, the slide member has to be inserted from the end of the base member into the dovetail-type guide means. Accordingly, when a slide member is inserted, the slide member projects by a large distance beyond the base member and, thus, requires a large free space for manipulating the slide member. As a result, when several students or users of the transposition rule sitting next to each, for example, in a classroom, simultaneously manipulate the slide members, the students or users will interfere with each other.