See page 6 of the following Kriegsmarine Angriffscheibe (Attackdisk) thread. Hitmann shows reallife pieces of the angle solver side. It may not be exactly as is used in the mods (as the backside was seperate, and it is unknown how it looks) but it is not some make-believe modern invention Hitmann cooked up. Sliderulers where as common back then (well if you need to calculate some fancy stuff) as handheld digital calculators are today.
http://www.subsim.com/radioroom/show...=114351&page=6