Need to break one long column into smaller columns then apply function to each column

You don't really need to split up the long column in order to get averages over each set of 1500 rows, although it could be done using an INDEX formula, and then an average function for each column.

However, if you want to leave it as it is and just have the averages, then assuming the data is in column A starting at A1 (no headings), then you could put this formula in C1:

=AVERAGE(INDEX(A:A,(ROWS($1:1)-1)*1500+1):INDEX(A:A,ROWS($1:1)*1500+1))

This will give you the average for the rows 1-1500, and when you copy it down you will get averages for the rows 1501-3000, 3001-4500, 4501-6000, and so on in consecutive cells.

Hope this helps.

Pete

EDIT: Sorry - you should remove the final +1 from the formula, like this:

=AVERAGE(INDEX(A:A,(ROWS($1:1)-1)*1500+1):INDEX(A:A,ROWS($1:1)*1500))

I've shown it in red in the original formula.

Hope this helps.

Pete