Incorrect Value From Trendline Equation (Polynomial)

[Mr Uku]

Hi everyone, I've encountered an issue while creating a series of graphs within Excel. The trendline seems correct and follows the data points I have nicely. Unfortunately, when entering the value for x into the equation manually in Table 1, the values differ greatly, percentage-wise. I have checked online to see if there might be a solution for it but I haven't found anything concrete and LINEST doesn't seem to work.

Is there any way in which I can get the equation to return an answer close to what is displayed in the graph?

Any help would be greatly appreciated!

Air Permeability Calculations.xlsx
	H	I	J	K	L	M	N	O	P
19
20
21
22
23
24								Table 1
25								Percentage Comparison
26								Equ. Value	% Diff.
27								34.9980141	0.00567386
28								89.925499	-156.929997
29								159.857213	-59.8572134
30
31
32
33
34
35
36
Polynomial Solution

Cell Formulas
Range	Formula
O27	O27	=(0.039*(($G9)^3))-(1.0141*(($G9)^2))+(11.055*$G9)
P27:P28	P27	=100-(($O27/$B$9)*100)
O28	O28	=(0.039*(($G15)^3))-(1.0141*(($G15)^2))+(11.055*$G15)
O29	O29	=(0.039*(($G17)^3))-(1.0141*(($G17)^2))+(11.055*$G17)
P29	P29	=100-(($O29/$B$16)*100)

 

[Mr Uku]

It turns out that I am at fault - I was comparing the values in the wrong column the entire time

I also managed to use the LINEST functions to "recreate" my trendline's equation to a high degree of accuracy.

Apologies if anyone wasted their time.