Newcomers, if you don't know CapnScurvy he's spent more time with the stadimeter/periscope system than you've spent playing the game. Matter of fact, probably more than I have spent playing the game. He's by far the authority on this area of Silent Hunter 4 and y'all need to pay attention to his posts. Even including the supermodders, there's nobody who has contributed more to the community and more to the great state of SH4. Scurvy isn't a prima donna and he shoots from the hip. Accurately I might add.
Capn, I still bet the reason for the "errors" was rounding error coming from the use of slide rules to perform all the calculations. Try it yourself and what you read off the slide rule is what they use for an answer. Real geeks at the time would never perform an arithmetic calculation unless a gun were pointed at their head!