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

I guess I should clarify the accuracy required. These are high precision
Load Cell calibrations which we hope are in the order of 0.005 percent
accurate. While the curve is almost linear, the second order is very
important and the third less so, but we supply the equation to our
customers. It would be nice to know that it is accurate.
--
Jim
National Research Council of Canada


"Gary''s Student" wrote:

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