While trying to fit a TGraph with a “pol3”, I get (note how it “jumps”):

[code]root [18] g->Fit(“pol3”)

Minimizer is Linear

Chi2 = 2075.61

NDf = 464

p0 = 4.89194e+06 +/- 753524

p1 = -7394.77 +/- 1142.6

p2 = 3.72553 +/- 0.577519

p3 = -0.000625518 +/- 9.72989e-05

(class TFitResultPtr)141375584

root [19] g->Fit(“pol3”)

Minimizer is Linear

Chi2 = 2099.3

NDf = 464

p0 = 2.10406e+06 +/- 495473

p1 = -3167.38 +/- 751.307

p2 = 1.58883 +/- 0.379741

p3 = -0.000265534 +/- 6.3978e-05

(class TFitResultPtr)137580960

root [20] g->Fit(“pol3”)

Minimizer is Linear

Chi2 = 15384.7

NDf = 464

p0 = 4.07854e+07 +/- 5.93457e+06

p1 = -61821.9 +/- 8998.9

p2 = 31.2352 +/- 4.54841

p3 = -0.00526026 +/- 0.000766302

(class TFitResultPtr)145594664

root [21] g->Fit(“pol3”)

Minimizer is Linear

Chi2 = 2262.49

NDf = 464

p0 = 8.40135e+06 +/- 1.03222e+06

p1 = -12716.3 +/- 1565.21

p2 = 6.41525 +/- 0.791122

p3 = -0.00107867 +/- 0.000133286

(class TFitResultPtr)140055624[/code]