Sieber wrote: "N.B. All the exercises are to be sung at first on various vowels - (a,e,i, o, u) and later on the syllables written under them. Do NOT observe at first, the shading directions (crescendo and diminuendo) but sing each exercise in a quiet and smooth way and as legato as possible. The tempo to be employed depends on the needs and ability of the singer. At every rest and at every breathing mark (+), breath must be taken and it may also be taken (if required ) at the commas (')".