a1 = 5.000000  a2 = -3.420000  a3 = 0.003840  a4 = 0.265000
fitted parameters' values:
a1 = 9.748152 ± 0.07255555
a2 = -0.2772526 ± 0.0006266139
a3 = 0.001157768 ± 5.810196e-06
a4 = 0.2185241 ± 0.01019515
cov(a1,a2) = -2.279261e-05
cov(a1,a3) = 1.419865e-08
cov(a1,a4) = -0.000769909
cov(a2,a3) = 2.722752e-09
cov(a2,a4) = 4.30248e-06
cov(a3,a4) = 1.492993e-06
chi^2 = 519.01
ndf = 566
chi^2_reduced = 0.91698
p probability = 0.92181