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

parameters
offset a	slope b
-2.16262e-06	0.000125834

Covariance matrix
3.83047e-14	-1.61938e-12
-1.61938e-12	6.95709e-11

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.16	2.85112e-06	1.40382e-07	Ba133
80.98	6.99679e-07	2.5108e-08	Ba133
