A tone is not a psalm number. It is the mode in which that week's resurrection hymns are sung — the whole week's Vespers, Matins and Liturgy are set in one tone.

There are eight tones, and they change each week. The cycle opens with the first tone on Thomas Sunday after Pascha and returns to the first every eight weeks; Bright Week itself has no tone of its own. A new tone begins on Saturday evening, with the new church week.

The Psalter is divided into twenty kathismata and, by the usual rule, is read through once a week. Appointed for this day:

This is the usual rule. In Great Lent the Psalter is read twice a week, and the kathismata are divided differently.