Your solution may be ill-conditioned. Plot your data and it appears nearly
linear.

If you fit using only two parameters (slope & intercept) you get
a = -9.62307E-05
b = 0.000329459



2499.89 -0.24042 -0.240236766 3.35746E-08
4499.83 -0.43274 -0.432692441 2.26186E-09
6499.77 -0.62507 -0.625148116 6.10209E-09
8999.69 -0.86558 -0.865717228 1.88316E-08
11499.83 -1.10609 -1.106307511 4.73112E-08
13499.91 -1.29861 -1.298776658 2.7775E-08
15999.74 -1.53922 -1.53933711 1.37148E-08
18499.93 -1.7798 -1.779932205 1.74781E-08
20500.05 -1.972495 -1.972405201 8.06385E-09
21999.93 -2.11685 -2.11673974 1.21573E-08
2499.89 -0.2404 -0.240236766 2.66453E-08
4499.83 -0.43274 -0.432692441 2.26186E-09
6499.77 -0.62507 -0.625148116 6.10209E-09
8999.69 -0.865535 -0.865717228 3.32071E-08
11499.83 -1.106125 -1.106307511 3.33104E-08
13499.91 -1.29861 -1.298776658 2.7775E-08
15999.74 -1.539235 -1.53933711 1.04265E-08
18499.93 -1.77985 -1.779932205 6.75762E-09
20500.05 -1.97241 -1.972405201 2.30297E-11
21999.93 -2.11683 -2.11673974 8.14689E-09
2499.89 -0.24043 -0.240236766 3.73393E-08
4499.83 -0.43277 -0.432692441 6.01539E-09
6499.77 -0.62515 -0.625148116 3.55003E-12
8999.69 -0.865625 -0.865717228 8.50604E-09
11499.83 -1.106175 -1.106307511 1.75593E-08
13499.91 -1.29868 -1.298776658 9.34286E-09
15999.74 -1.53924 -1.53933711 9.43036E-09
18499.93 -1.779895 -1.779932205 1.38419E-09
20500.05 -1.97244 -1.972405201 1.21097E-09
21999.93 -2.11684 -2.11673974 1.00521E-08
4.4277E-07
Where the third column is the linear model and the fourth column is the
square of the error.

It may not be meaningful to go beyond two parameters.
--
Gary''s Student


"JimK" wrote:

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