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

parameters
offset a	slope b
-1.05916e-05	0.000612697

Covariance matrix
1.08024e-12	-4.55344e-11
-4.55344e-11	1.95169e-09

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.18	1.38492e-05	7.43706e-07	Ba133
81	3.36389e-06	1.35975e-07	Ba133
