Thought you wanted all the results neatly bunched at the top, w/o any gaps ?
<g
The earlier suggestion would do just that

Anyway, if you really want the results listed in the manner as per your
response below, where the values to be averaged are running in B1 down

Put in C1:
=IF(MOD(ROWS($1:1)-1,15)=14,AVERAGE(OFFSET(B1,,,-15)),"")
Copy C1 down as far as required. This will return the results exactly as
indicated in your response.
--
Max
Singapore
http://savefile.com/projects/236895
xdemechanik
---
"Bec" wrote:
Hi Max

Thanks for the formula. I was able to make it work using columns not rows.
How do I make the starting value change every 15 cells automatically? My
spreadsheet is set out like below.

TIA
Bec

20/08/2007 19:22 0.7950
20/08/2007 19:23 0.8090
20/08/2007 19:24 0.8600
20/08/2007 19:25 0.8600
20/08/2007 19:26 0.8420
20/08/2007 19:27 0.8500
20/08/2007 19:28 0.8450
20/08/2007 19:29 0.8520
20/08/2007 19:30 0.8540
20/08/2007 19:31 0.8470
20/08/2007 19:32 0.8480
20/08/2007 19:33 0.8510
20/08/2007 19:34 0.8480
20/08/2007 19:35 0.8580
20/08/2007 19:36 0.8560 0.8450
20/08/2007 19:37 0.8560
20/08/2007 19:38 0.8500
20/08/2007 19:39 0.8540
20/08/2007 19:40 0.8560
20/08/2007 19:41 0.8310
20/08/2007 19:42 0.8400
20/08/2007 19:43 0.8410
20/08/2007 19:44 0.8530
20/08/2007 19:45 0.8550
20/08/2007 19:46 0.8570
20/08/2007 19:47 0.8310
20/08/2007 19:48 0.8430
20/08/2007 19:49 0.8540
20/08/2007 19:50 0.8360
20/08/2007 19:51 0.7940 0.8434