Hi,

Why not average column C only if there are entries in columns A & B

=AVERAGE(IF(A1:A20<"",IF(B1:B20<"",C1:C20)))

This is an array formula which must be entered by pressing CTRL+Shift+Enter
'and not just Enter. If you do it correctly then Excel will put curly brackets
'around the formula {}. You can't type these yourself. If you edit the formula
'you must enter it again with CTRL+Shift+Enter.

Mike

"Laurizio" wrote:

Hi,

I'm trying to generate a list of timespans where I eventually want the
average. The timespans (column C) is calculated by formula (B-A). This list
will be constantly updated so I have prepared the formulas for the cells even
though the dates aren't filled in.

An illustration of my spread sheet is:

Row A B C
1 2009-01-01 2009-01-10 9
2 2009-01-01 2009-01-20 19
3 2009-01-05 2009-01-10 5
4 2009-01-15 2009-01-15 0
5 0 (b5-a5)
6 0 (b6-a6)
...


When I want the average so far it counts with the rows not yet filled in as
well (row 5-6 in the example). My question is; Can I ignore the rows not yet
filled in in any smart way? One option that I have tried is to ignore
everything less than 1 when doing the average formula but then I risk missing
the few ones where the timespan equals 0 (C4 in the example).


Thx for your support!