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

parameters
offset a	slope b
-7.39966e-06	0.000434264

Covariance matrix
5.1483e-13	-2.16652e-11
-2.16652e-11	9.27733e-10

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.16	9.92752e-06	5.12745e-07	Ba133
80.98	2.49035e-06	9.58868e-08	Ba133
