[Ifeffit] Find white line position

Dear all, I have a question about one of the useful function, "find white line position" in Athena. Could anyone tell me how Athena find the white line position by this function? In other words, I would like to know the algorithm to find the white line position in Athena. Thank you very much for your help, in advance. Best regards, Hiroshi Oji -- Hiroshi Oji, PhD. NUSR & AichiSR, Japan E-mail: h.oji@nusr.nagoya-u.ac.jp