Always keep in mind that XUV spectrometers
do not have an accurate `standard' wavelength calibration,
and therefore
absolute wavelength measurements are subject to various uncertainties.
Normally spectra have to be calibrated using observed chromospheric
lines (if observed) or any other lines.
The issue of rest wavelengths is a serious one.
For accurate analyses, the values found in the databases
are not always the best ones to be used.
CHIANTI normally uses the values from the NIST database,
which in turn is a compilation of values found in the literature.
It is necessary to go back and read the original literature
to understand the uncertainties associated with measurements.
