Hi Peter,

As often in astro papers, mathematical developpement are in the Appendix.

See p10 for sigma(EW) formula.

More recently in 2006, Vollmann and Eversberg wrote a short paper with some improvements that makes continuum S/N less important and then, sigma(EW) a bit less overestimated:

https://arxiv.org/abs/astro-ph/0606341

Benji