Average of selected cells, array required?

Hi,

thanks for reading, it has been a few years since I have had to do anything like this in Excel, so I'm very rusty.

My problem is this: I have been measuring crystals length and breadth, I now have over 4000 rows of data and I would like to extract the average size for each individual crystal (not overall average of the 4000+ measurement).

E.g. In column A the data in cells A2 and A3 relates to one crystal, A4 and A5 the next, A6 and A7 the next and so on. Now I know how to get the average using formulas =AVERAGE(A2,A3), =AVERAGE(A4,A5), =AVERAGE(A6,A7) but when I copy this down it doesn't automatically go to =AVERAGE(A8,A9), =AVERAGE(A10,A11) and so on, how do I make it do this? I remember using an array to select every other cell a few years back, is it something like this I need to do?


Thanks.