This is Life!: Revolutions Around the Cruciform Axis

Liturgical Math

From Liturgical Math:

How to Find the Resurrectional Matins Gospel Lesson
Divide the number of the Sunday after Pentecost by eleven and the remainder will be equal to the number of the Matins Gospel reading for the day.

For example, if it is the 21st Sunday after Pentecost, you divide 21 by 11. The remainder is ten, so the Matins gospel is number ten.

How to Find the Tone of the Week

Take the number of the Sunday after Pentecost, subtract one, and divide by eight. The remainder is equal to the tone of the week.

Expression (P = Week after Pentecost, T = tone of the week): (P-1)/8 = _ RT

For example, if it is the 21st week after Pentecost, you use this expression:

(21-1)/8 = 2 R4

Therefore, tone of the week is Tone Four. If there is no remainder, then the tone of the week is eight.