Hitman is our own esteemed submarine technology history professor.
I don't think he is onr in real life though. He's the best to give an answer on your question as it relates to what was and is not historical realism. It might take him awhile though to get out of those stuffy museum archives.
He also worked together with OLC and Joegrundman to develop the tools you use in OLC's gui mod.
I have seen a german website of a guy (link below) that worked at a real sub museum in germany. He had information about some of the technology back then. The methods used in OLC's attack periscope reasembles quite accurately the desciption of german attack periscope on that site. Appearantly the germans developed a split prism mechanism into their periscopes (like is used in SH4 in the american sub) but also had a double function (as far as I know the americans weren't as clever ;p ) to also allow to measure the AOB based on the apperant length or aspect ratio (length over height) of the target in view. So the attack periscope seems quite realistic. Maybe it is not a computer terms of our modern definition but it certainly computed range and angle on the bow based on visual input by the observer.
As for the other gadgets, I'm not really sure what you mean. OLC included a calculator disk to help calculate bearings, course, AOB and such. Hitman found those real disks somewhere and started this whole project of replicating them (also the backside to help with speed/range/time/angle calculstions ) as handheld tools and they where shortly thereafter made into digital form , as a seperate program but also as a mod useable ingame. The way he suggests to measure speed by making a fixed line with your periscope centerlinge is also true to the technology as used back then. ('Feste linie im raum'= fixed line through space, in the link below)
http://www.uboot995.homepage.t-onlin...__zubehor.html
But appearantly those technologies werent used on all boats during all years of the war. Or commanders felt like preffering their own judgements by eye.
Anyway, Hitman where are you!!!