I don't think the size of the range has anything to do with it. I could not
replicate your problem. Probably formatting.

--
Don Guillett
Microsoft MVP Excel
SalesAid Software

"Adam Lawrence Acoustics" <Adam Lawrence
wrote in message
...
Hi,

I've used SumIf quite a lot to summaraise data in a spreadsheet, which has
always worked fine, however I'm now trying to sum ranges over some 16,500
data points, and now I have this much larger range the calculations dont
seem
to work, whereas they always have over much shorter ranges.

I'm just testing with a couple of numbers to see that it works and these
tests are not working.

Two examples:

I expect this to return 10
=+SUMIF(GridCalcs!Z$3:Z$17001,"=0.1",GridCalcs!$D $3:$D$17001)-SUM(AG13:AG$15)
because cell Z16544 = 0.1 and Cell D16544 = 10.

I expect this to return 100
=+SUMIF(GridCalcs!BC$3:BC$17001,"<=-0.1",GridCalcs!$E$3:$E$17001)-SUM(O19:O$21)
because cell BC16545 = -0.1 and Cell D16545 = 100

Both sums actually return zero. All the other values in column D are set
to
0 for the purposes of the test. The problem only seems to occur with the
0.1
and -0.1 values, and of course if I set up a simple test in another
workbook,
that works fine.

Oh, this is Excel 2003, SP2. The spreadsheet is trying to do quite a lot
of
results processing for me(!). The file size is a shade under 200MB.

Any thoughts?