I really wonder which indefinite article is the righter one about the scientific abbreviation "SEO". According to these opinions over there (<a href='http://www.seo-forum-seo-luntan.com/seo/%27an-seo%27-or-%27a-seo%27-which-indefinite-article-is-the-right-one' target='_blank' rel='nofollow'>http://www.seo-forum-seo-luntan.com/seo/%27an-seo%27-or-%27a-seo%27-which-indefinite-article-is-the-right-one</a>/) according to the spelling it is "a", but according to the pronunciation it is "an". Are they both right or not? How do you think?