What does this Forumula Do?

I'm new to formulas and am stuck on what does this formula do?

MOD(13-INT((RC[-4]-DATE(2001,12,30)+7)/7)/4,13)

My worksheet imports data. From this data this formula refers to a chart that is set up like this:

Q1-2003 4/19/03 7 67.50
Q2-2003 7/12/03 5 32.00
Q3-2003 10/4/03 11 46.00
Q4-2003 12/27/03 12 14.50

This formula (I think) refers to the above table compares the date, then inserts the information from column four.

The problem is understanding this formula to update the information.

Thanks for you help.

I think someone was trying to calculate the month of a year - if so, it will not always give the right answer.

To calculate the month see enclosed zip-file examples:

Ola Sandström