Hello
I am using Linest as follows:
=LINEST(C2:C31,B2:B31^{1,2,3},,TRUE)

Highlight 4 cells, cut and paste this equation into the window and do a
control-shift-enter to get out the array of the terms A, B, C, & D in the
curve fit equation:

Y = A + Bx +Cx^2 +Dx^3

As mentioned in the other reply, my data is almost a linear fit, but due to
the accuracy required, I need more terms than Y = A + Bx
Cheers
Jim
--
Jim
National Research Council of Canada


"Bernie Deitrick" wrote:

Jim,

How are you using LINEST? LINEST returns m and b, neither of which is greatly affected by the
change from -0.24042 to -0.240419....

I get:

Y = -9.622911E-05 + 0.000351*X

and

Y = -9.622914E-05 + 0.000352*X

as the straight lines returned by LINEST using your data....

HTH,
Bernie
MS Excel MVP


"JimK" wrote in message
...
The Linest Function has severe errors when curve fitting my data as follows:

X Y
2499.89 -0.240420
4499.83 -0.432740
6499.77 -0.625070
8999.69 -0.865580
11499.83 -1.106090
13499.91 -1.298610
15999.74 -1.539220
18499.93 -1.779800
20500.05 -1.972495
21999.93 -2.116850
2499.89 -0.240400
4499.83 -0.432740
6499.77 -0.625070
8999.69 -0.865535
11499.83 -1.106125
13499.91 -1.298610
15999.74 -1.539235
18499.93 -1.779850
20500.05 -1.972410
21999.93 -2.116830
2499.89 -0.240430
4499.83 -0.432770
6499.77 -0.625150
8999.69 -0.865625
11499.83 -1.106175
13499.91 -1.298680
15999.74 -1.539240
18499.93 -1.779895
20500.05 -1.972440
21999.93 -2.116840

D C B
A
4.384643E-17 -4.849642E-12 -9.613158E-05 -7.173873E-05

If you change the first 'Y' value to -0.240419 (the real value), the Linest
Equation blows up and is wrong, (Value of 'D' is zero). The results are
below:
D C B A
0 -4.83784E-12 -9.61317E-05 8.03804E-05

Is there any fix by Microsoft in the works or is there something I can do to
ensure data sent to the customer is correct?
--
Jim
National Research Council of Canada