Put the value you want to use into another cell, say E1, and use this cell
reference in the formula:

=FORECAST(30,A2:A29,B2:B29)+FORECAST(E1,C3:C29,B3: B29)

- Jon
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Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. - http://PeltierTech.com
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"Saxman" wrote in message
...
Saxman wrote:

x y
0 25
1000 26
2000 27
3000 28
4000 28
5000 29
6000 30
7000 31
8000 32
9000 32
10000 33
20000 41
30000 49
40000 57
41000 58
42000 59
43000 60
44000 60
45000 61
46000 62
47000 63
48000 64
49000 65
50000 66
100000 106
300000 268
500000 430

It looks like the FORECAST function will do similar from the given data
above.
There is an example in the help files. From the function below which is
in cell
B31, how do I create a data entry cell without have to alter the value in
the
function below? (In this example 10000).

=FORECAST(30,A2:A29,B2:B29)+FORECAST(10000,C3:C29, B3:B29)

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