the centuries, Byzantine music notation became increasingly more specific.
That is to say, later composers chose to write particular musical phrases
with more notes than those of earlier composers. In other words, the
later composers wrote out ornamental formulas in full, whereas in the
past, these would have been left to the skill and experience of the
chanters. This clarification did not purport to add anything new to
a given melody, but rather it spelled out the way in which the tune
was intended to be chanted in order to eliminate erroneous interpretations.
Even today, a chanter following Byzantine notation is still expected
to "interpret" a musical phrase based on the oral tradition he has inherited
from his mentor. Interpreting a musical phrase entails chanting a tone
with a certain Úlan or adding notes to a phrase.
Transcribed literally into Western notation, this phrase
would appear simply as:
However, most chanters
with even a rudimentary knowledge of the oral tradition would perform
it in the following way:
The ison, or tonic note, of the melody is indicated by a capital letter written above the staff. This note is to be held until another letter above the staff changes the pitch of the ison. If there is more than one person holding the ison, they should take breaths at different times so that there are no breaks, even if there is a rest in the melody. Those who hold the ison may do so in octaves, but they need to be careful not to sing louder than those performing the melody. Ideally, ison holders should pronounce the words simultaneously with those singing the melody. However, the prevailing practice today is to hold a sustained schwa sound [ə] instead, since this neutral vowel does not clash with the vowels in the sung text. The abbreviation "Un." means that the ison singers should join in unison with the melody. The ison is almost always chanted at a pitch lower than or equal to the pitch of the melody. When the ison needs be pitched in the lower octave only, a downward-pointing arrow follows the ison note (for example, BÔ). An ellipsis following the ison note (for example, C.) means that the ison should be held without stopping at the upcoming rest in the melody. Since Byzantine music is not based on absolute pitches but on the pitches of Νη-Πα-Βου (Do-Re-Mi) etc., which are relative, the entire melody may (and should) be transposed to a pitch that fits the tessitura of the singers. The tone Νη (Do) is always fixed at C throughout this anthology. Although this convention facilitates sight-reading, it makes several melodies too high for some people (especially for baritones and female voices) unless these melodies are transposed.
Tempo marks are provided merely as guidelines; they may be altered to accommodate local requirements. The tempo of the cherubic hymn may need to be altered significantly, depending on how much time the priest spends reading the prayers before the great entrance. Following current practice, the words "that we may receive the King of all" (the concluding words of the first part of the cherubic hymn) are usually chanted in a rapid monotone. But if the choristers reach this phrase before the priest is ready for the great entrance, they may bide time by chanting this phrase according to the music. To facilitate this synchronization, the approximate duration of each cherubic hymn is provided so that the choir may alter its tempo accordingly. The duration is given in three parts. For example, if the duration is: "4:30 + 1:00 + :45," this means that the first part of the cherubic hymn lasts four and a half minutes, the phrase "that we may receive the King of all" lasts one minute, and the final part, which is chanted after the great entrance, lasts 45 seconds.
 cf. Tillyard, H.J.W., Handbook of the Middle Byzantine Musical Notation, Monumenta Musicae Byzantinae, Subsidia 1, Fasc. 1, Copenhagen, 1935, pp. 14-16.