I want to use an interpolation table in excel. When I type in the value, I
want excel to look up the closest two values in the table and calculate the
corresponding value.

Some kind of an overkill - but obviously tested and
reliable (no guarantee but I found it very helpful):

http://www.codeproject.com/macro/InterpolationAddin.asp

HTH,
Bernd

One way to try
(for a one way interpolation)

Suppose you have the reference table
below in A1:B3

X Y
100 1.5
200 2.8
300 4.5

If you earmark say,
cell D1 for input of X values

then you could put in E1:

=IF(ISNA(MATCH(D1,A1:A3,0)),FORECAST(D1,B1:B3,A1:A 3),INDEX(B1:B3,MATCH(D1,A1
:A3,0)))

E1 will return the exact Y value from the reference table
if D1 contains an X value which matches (viz.: 100, 200, 300)

If D1 contains unmatched X values, say: 150,
E1 will return the interpolated value of: 2.183

Adapt to suit
--

And for a 2 way interpolation set-up to play with,
try this recent post: http://tinyurl.com/676wu

--
Rgds
Max
xl 97
---
GMT+8, 1° 22' N 103° 45' E
xdemechanik <atyahoo<dotcom
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"Elif" wrote in message
...
I want to use an interpolation table in excel. When I type in the value, I
want excel to look up the closest two values in the table and calculate
the
corresponding value.