Simplify the following text for a Grade 6 native English-speaking person.
Original: The Circle of Fifths , first described in 1728 by Johann David Heinichen in his book Der General-bass , has been used ever since as a means of illustrating the relative harmonic distance between musical keys ( Drabkin 2001 ) .
Simplified: The Circle of Fifths was first described in 1728 by Johann David Heinichen in his book Der General-bass .