New Update 22 january 2019 :
For persicope RAOBF discs users, in ARB widegui, zoom at x1.5, x6 (and now x12) are functional and the measures are correct
With CTRL + mouse wheel, you can go to max zoom x12 in Obs periscope and Attack periscope. (normal zoom levels without "Ctrl+mouse wheel" are unchanged)
Updated link 22 January 2019 to Post 1 :
http://www.subsim.com/radioroom/showthread.php?t=239167