I previously asked for help with this:

In Excel2000, I would like to create a dynamic year-to-date formula. I
have the following data starting in row 3 and going from column A to
column X:


Jan Actuals Jan Budget Feb Actuals Feb Budget
100 200 300 400


I would like to use cell A1 as an input cell for the month ( ex. Feb =
2). I would like the formula to lookup the month and then tell me how
much Feb YTD Actuals are ( in this example = 400 ). All I want to
change each month is the input cell in A1 and have the formula
automatically give me the results.


Someone responded with this formula:

=SUMPRODUCT(--(MOD(COLUMN(OFFSET($A$2,,,,CHOOSE($A$10,1,3,5,7,9, 11,13,15,17,19,21,23))),2)=1),OFFSET($A$2,,,,CHOOS E($A$10,1,3,5,7,9,11,13,15,17,19,21,23)))

Can someone plaes explain this formula. It works perfectly but I don't
understand it.

Thanks