The nominals are the set of letter-names, numbers, or other symbols which are used to identify the basic scale in the notation of a particular tuning system. An equivalence-interval is generally recognized, which limits the nominals to a small set.
The standard Western diatonic scale forms the basis of Western musical notation, as follows:
Because of its familiarity, the diatonic system of note-naming is often pressed into service (with or without modifications) to designate non-diatonic tunings, but most tuning theorists prefer to design different systems of nominals which are appropriate to the characteristics of particular tunings.
An example of a non-diatonic system of nominals is Graham Breed's decimal notation, using integers 0 ... 9 as the nominals, for notating tunings belonging to the miracle family.