After having identified a few lines with the Identify window, click the
button in the Main window. The Wavelength
Calibration window appears. The associated parameters can be set and a
preliminary wavelength calibration is performed on the central row
YSTART by clicking on 
. The button 
allows to remove calibration lines from the dispersion solution
interactively, while 
estimates the dispersion
relation for the complete spectrum. The button 
performs a two-pass calibration.
Results can be checked with the buttons located at the bottom of the
Wavelength Calibration window. 
plots the
dispersion relation, 
plots the residuals,
plots the lines identified during the calibration
process. These three functions are by default performed on the central
row of the spectrum. The button 
plots the
residuals as a function of the Y-position for a line selected in a
wavelength list.
Figure: Wavelength Calibration window