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

parameters
offset a	slope b
-3.39474e-05	0.00196624

Covariance matrix
1.38658e-11	-5.78444e-10
-5.78444e-10	2.46201e-08

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.17	4.4632e-05	2.63692e-06	Ba133
80.98	1.09138e-05	5.35441e-07	Ba133
