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

parameters
offset a	slope b
-2.25931e-06	0.000128619

Covariance matrix
3.81143e-14	-1.61652e-12
-1.61652e-12	6.95803e-11

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.16	2.86542e-06	1.40567e-07	Ba133
80.97	6.66692e-07	2.39716e-08	Ba133
