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

parameters
offset a	slope b
-3.45559e-06	0.000196461

Covariance matrix
9.03968e-14	-3.82924e-12
-3.82924e-12	1.64663e-10

used data points for fitting
energy [keV]	efficiency	efficiency error	nuclide
53.17	4.37371e-06	2.1611e-07	Ba133
80.96	1.01624e-06	3.7252e-08	Ba133
