Gidday

I am seeking a bit of help with what the "-{1,7}" does/means in the
following formula;
=ABS(IF((DATE(YEAR(C3),MONTH(C3)+1,DAY(C3))),(C3)-(DATE(YEAR(C3),MONTH(C3)+1,DAY(C3)))-SUM(INT((WEEKDAY((DATE(YEAR(C3),MONTH(C3)+1,DAY(C3 )))-{1,7})+(C3)-(DATE(YEAR(C3),MONTH(C3)+1,DAY(C3))))/7)),""))

The forumal works out the number of workdays in a month where C3= 1/1/2007
and the return answer is 20

I look forward to your responses.