The following can be ignored and/or whatever, it is just a quibble and this after all is a game.
I blame Hitman, as his excellent work has turned me into a periscope snob.
On NYGM, ARB shows interesting scope zoom settings. 5x and 10x on the attack scope and 4.5x and 11x on the observation scope.
Around 40-41 they started making scopes a similar specification.
1. No whiz-wheel / stadimeter: visual only
2. 1.5x and 6x zoom on both attack and observation/night scopes. Example below.
3. Trivia, this photo of the observation/nightscope is a monicular eyepiece, the black disk above was an option to fit a binocular eyepiece resulting in an inverted "V" as seen below.
4. I now use silent editor to change both periscopes to 1.5x and 6x zoom settings as this is what I am used to for computing range.
5. With that, I think it is important to add a 3rd zoom setting where you see fit like 15x for the topside binoculars ....just to save your eyesight.....(ARB already has this eyesight saving feature in biono and uzo).
Charts from actual German U-boat procedure that give you a visual picture of what you are seeing to predict range in regard to 1.5x and 6x zoom settings. via Hitman
Anyway...ARB is a lovely and fun add on for the game. Very nice.