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I have the graticule scaled correctly for low power setting 1.5x but not so much at 6x.
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The graticule was fixed for 1.5x zoom, it didn't change at all when switching to 6x.
1.5x was used in german (And US, and British) periscopes because that magnification gave the better feeling of the natural size of objects when looking with naked eye. That helped considerably estimating distance to them and keeping a good picture of the tactical situation. High power zoom in turn was used just for identifying details and gathering info about the target, never for estimating distance.
From the UBoat Commander's Handbook:
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130.) For computing the range, the 1 magnification should be used in the periscope. With the 6-fold magnification, no estimation of distance is possible, on account of the monocular optical system of the periscope.
As a matter of principles the 6-fold magnification of the periscope should always only be used temporarily, in order the better to observe details of the enemy ship, as, for example, in computing its course and speed, but never for the actual attack at close range.
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Interestingly, the US periscopes were actually set for using at 6x
The reason is that prewar doctrine considered it too difficult to approach an escroted target because of ASDIC, and submarines were thus expected to shoot from extreme ranges (In itself the reason why the fantastic american TDC was developed). In the US periscopes, like the picture shown above by Bilge_Rat, the big mark corresponds to 1 degree, the small ones to 1/4th of a degree at 6x magnification (Thus the divisions seen)