Used file for the fit: SDD_normalized-Efficiency_point-source_with-air_all-levels.csv

parameters
offset a	slope b
-2.60695e-06	0.000154557

Covariance matrix
1.50414e-13	-3.57368e-12
-3.57368e-12	9.42955e-11

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.16	3.47532e-06	1.73011e-07	Ba133
26.34	2.70168e-05	1.84297e-06	Am241
33.2	1.39916e-05	1.2665e-06	Am241
59.53	2.59715e-06	1.75548e-07	Am241
