Sum function that skips rows when dragged down

[lmmorrison]

Hello all,

I have a program outputting data to an Excel file into a single column of 4 rows per measurement. I'd like to sum some of these and put the results in a summary table on the same sheet, but I only need the top two rows or the bottom two rows at a time for each measurement. For example:

_B8: 1a ...... _E8: =_B8+_B9 (1a+1b)
_B9: 1b ...... _E9: =B12+B13 (2a+2b)
B10: 1c ...... E10: =B16+B17 (3a+3b)
B11: 1d
B12: 2a
B13: 2b
B14: 2c
B15: 2d
B13: 3a
B14: 3b
B15: 3c
B16: 3d

This should go on for hundreds, maybe thousands of rows, so I'd like to get it to where I can just Ctrl-Enter the data table. How can this be done? I've been playing around with the OFFSET function, but I haven't quite figured it out.

Thanks.