There can be a difference in speed writing to cells when an object is
selected rather than a cell, and better still to select an empty cell. I'm
not aware though of there being any difference if the application is/not
active in Windows.

When reading and (particularly) writing to cells it's best to to use an
intermediate array and assign/write in one go (but if more than say 100k
cells do it in chuncks)

' read
dim i as long, j as long
Dim arr
arr = range("A1:C10")

for j = 1 to ubound(arr)
for k = 1 to ubound(arr,2)

' process(arr(j,k)
next
next


' write
Redim arr(1 to myRows, 1 to myColumns)

' populate the array

dim rng as Range

set rng = "Range("a1")

set rng = rng.resize(ubound(arr), ubound(arr,2))

rng.Value = arr


(not tested, typos a distinct possibility!)

Regards,
Peter T












"Andrew" wrote in message
...
I have a loop that runs really fast at first (15+ records per second),
but then continually slows down (2 per second). It seems to be after
2000-3000 records. It gets much slower when excel is not selected and
speeds up when it is selected. I read some information on optimization
and it helped speed it up at the beginning, but the problem of slowing
down still occurs.

Has anyone heard of this?

By the way, I read records from sheets and write back to them. I also
have a SQL query in a sheet that refreshes for each record.

Any suggestions are welcome.