Among the best of my experiences on this forum has been becoming friends with many collectors, including especially Antonio Gomes from Portugal.
Tony, who posts as clepsydra on the forum, is a terrific guy, quick-witted and always with bright and frequently penetrating insights. He's also a true collector of vintage IWC watches and a serious student of horology.
Tony researched and wrote a truly scholarly article article entitled "IWC Vintage Portuguese: Identification of the Hallmark on ref. 325". The article was published in the April 2015 issue of the British Horological Journal. I'm please to let you know that you can view and download this great work at www.iwcforum.com/IWC.pdf.
The first page is shown below, but due to size restrictions with this forum's software it's best to view and save the PDF version linked above.
Hurrah!