Each part may be performed by four to eight instruments, which are all capable of sustaining a note with identical intensity. The written notes can only be read is treble clef but can be placed anywhere in the register. The composition of the groups of instruments within the individual parts should always be varied both as far as the setting and the proportion of the high, middle and low instruments within one and same part are concerned. The various groups may also consist exclusively of wind or string instruments. It is extremely important to precisely keep the durations and the dynamics. For the duration of a note all factors must remain identical. Accidentals always govern only the note they preceed (even within one bar).