A term used by Fokker to indicate the 1/1 of a utonality; that is, the high pitch that forms the 'root' of a chord composed of members from the subharmonic series, all of which have a numerary nexus.
The guide-tone is the LCM or LCD of a set of ratios. It can always be found on a lattice diagram as a point in one of the corners of the structure.
See "euler genus" for examples.
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