2452 20160701171705.0 ASTROimport-609 Hensberge, H. 1990 High Precision Wavelength Calibration of Echelle CCD Spectra Verschueren, W. Errors, Bias and Uncertainties in Astronomy 1990 335 http://esoads.eso.org/abs/1990ebua.conf..335H published in NONREF