Periscopes
 

I just tested the attack periscope for "Linier length" - and even tho the scope says "x4" it correctly represents 9° of FOV as the real attack scope did at x6.

I used a Dido class light cruiser at 1000 meters. The Dido is thankfully 156 meters long, wich is the same amount of meters that should be covered by 9° angular angle at 1000 meters distance.

in low power (x1 in SH5, and x1.5 in the real scope) the Linier Length are allso showing up correct. The Dido placed at 1000 meters range here covers 9 degrees (9 tics) as it should do.

So untill modded the periscope views at least give a correct representation of how big the ships looked through the scope, and vica virca the scope can be used to judge hight/lenght of targets.