There is a recent post in Ask an Apologist asking what week we are in for the Psalter. Fr. Serpa gave an excellent resource for finding the current day/week but what if it should become unavailable?

Here is the way I figured out: Remember simple division that does not break down to decimal places but keeps the "remainder" as a notation? Simply divide the week number (pay attention to this at Mass) by 4 and look at the remainder. 3 weeks out of 4, that remainder is exactly the week to use in the Psalter. Whenever there is no remainder, use week 4.

Examples:

Last week was the 15th week of Ordinary time. 15/4 = 3 R**3** (3rd week in the Psalter)

This is the 16th week of Ordinary time. 16/4 = 4 R**0** (4th week in the Psalter)

Next week will be the 17th week of Ordinary Time. 17/4 = 4 R**1** (1st week in the Psalter)

If you must use a calculator, you can look at the place after the decimal, but you'll have to memorize the interpretation.

.25 -> week 1 in the Psalter

.5 -> week 2

.75 -> week 3

(no decimal) -> week 4

Examples:

15th week: 15/4 = 3**.75** (3rd week in the Psalter)

16th week: 16/4 = 4█ (4th week in the Psalter)

17th week: 17/4 = 4**.25** (1st week in the Psalter)

Hope that's simple enough. If not, then the only advice I have is: don't get scrupulous about it.