not 100% sure
i think the extra bulk is due to the fact that the attack periscope is an "all heights" system -- i.e. the eye-piece stays at 1 level regardless of the height of the periscope, unlike the observation scope.
but, you may very well be right -- stadimeter mechanics may not have been attached to obs scope. hard to find details -- unless some has a u-boat technical manual. or works for zeiss.
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