Let's assume your x-values start in A1
The formula =INDIRECT("A"&ROW(A1)*10) in any cell (say E1) and copied down
the column will return the 10th, 20th, 30th x-values. And
=INDIRECT("B"&ROW(A1)*10) will return the y-values

The formula =INDIRECT("A"&(ROW(A1)-1)*10+1) in E1 and copied down the column
will return the 1st, 11th, 21st.... values

Alternatively, suppose you first x-value is in C5 and the last in C10000
Then =INDEX($C$5:$C$10000, ROW(A1)*10) in any cell and copied down the
column with give you the 10th, 20th, ... x-values

best wishes
--
Bernard V Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme
remove caps from email


"Mel_P" wrote in message
...
I have 33,000 pairs of values from a logger.
- Time, concentration
How do I plot (or extract) every 20th value (or some other defined
interval)?
Any ideas please (macro, VBA NOY manual selection).

I have tried past link row1, row10, row20 and dragging to extend the range
but this gives me row1, row20 row30 row2 row21 row31 etc

I want to end up with
row 1 data
row10 data
row 20 data

etc

Thanks. mel