If you have the daily averages in Col C and the first daily average in cell
C2 then try the below formula

=C2-LOOKUP(10^10,C:C)

OR

=ABS(C2-LOOKUP(10^10,C:C))

If this post helps click Yes
---------------
Jacob Skaria


"Andy_jm" wrote:

I have a spreadsheet with a column of data to which I add figures twice a
day. In another column I have a formula to calculate the daily average. What
I'm trying to do is to have another cell which automatically updates whith
the difference between the first and last daily averages.