The educational aid, serving the teaching of music, has at least two concentric disks suitably made of card, plastic or metal, which are fastened together so that they can rotate around their centre, and one or more circle scales are situated on the disks. One of the disks - the so-called basic disk (1) contains sectors (8) of identical central angle, and concentric circles (9) around the centre. In the segments - bowed trips - set up by the above mentioned concentric circles (9) and sectors (8), certain musical keys are written radiately, per sectors, going round, suitably in chromatic order. The so-called mask-disk (2, 3) which can rotate on the basic disk, contains sectors (8) which are identical with those on the basic disk in size and number, and concentric circles (9) which can be imaginary or real. There are look-over windows (5) on the places of notes and chords (harmonies) of different keys and their accords to be illustrated.
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