i mean i would not
want to change the values from 8 to 8.00000001 in the example.

Why is it a problem to add say 1*e-12 to only the last X & Y label/values.

Or are you saying you want to interpolate outside the range of data, If so
that's an entirely different matter, particularly if your data intervals are
non-linear, in either or both horizontal or vertical directions. That's
extrapolation and the method and formulas you would deploy would depend on
the type of data you have, how far you want to extend and probably other
factors.

Here's the origin of that big formula, paste following into H1:H13

5.5
2.5
=INDEX(xx,MATCH(H1,xx))
=INDEX(xx,MATCH(H1,xx)+1)
=INDEX(yy,MATCH(H2,yy))
=INDEX(yy,MATCH(H2,yy)+1)
=INDEX(data,MATCH(H2,yy),MATCH(H1,xx),1)
=INDEX(data,MATCH(H2,yy)+1,MATCH(H1,xx),1)
=INDEX(data,MATCH(H2,yy),MATCH(H1,xx)+1,1)
=INDEX(data,MATCH(H2,yy)+1,MATCH(H1,xx)+1,1)
=((H1-H3)/(H4-H3))*(H9-H7)+H7
=((H1-H3)/(H4-H3))*(H10-H8)+H8
=((H2-H5)/(H6-H5))*(H12-H11)+H11

Assumes named ranges xx, yy & data as I described before. You could also
name H1 as xi & H2 as yi (the inputs) so you can also use the big formula.

You could extend the last formula (in H13) to include an IF condition, or
maybe adapt some of the earlier formulas to your requirements.

When done you could assemble it all into your own jumbo formula, but ensure
it does not exceed the max formula length of 1024.

Regards,
Peter T

wrote in message
oups.com...
Thanks a lot. wow, it's realy amazing that there are people out there
with so much helping tendency. I really appreciate it. As peter told,
the long formula works well for the values with in the range. But the
following gives a little bit touble. Is there anyway to put this long
formula with IF conditions so that this will use HLOOKUP for the values
present and interpolate for the values not present. i mean i would not
want to change the values from 8 to 8.00000001 in the example.
xi = min(xx) and xi <max(xx)
So in the eg change 8 to 8.00000001
and similar re yi / yy

Thanks again
Regards
GP