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<p>[QUOTE=&quot;springfld.arsenal, post: 114552, member: 54&quot;]My own Latest WAG as to the purpose is that it was used to quickly measure the altitude of a pre-selected star that was close to the eastern or western horizon.&nbsp; That number and the exact time of observation, and some calculations will give the observer his longitude.&nbsp; Knowing longitude would have been particularly important for a U-boat involved in chasing or intercepting enemy convoys in the North Atlantic.&nbsp; A lot of that steaming was probably going mostly east or west.&nbsp; Latitude was much easier if you could see the star Polaris and the horizon, you get the altitude with a sextant and that&#039;s numerically about the same as your latitude.&nbsp; There&#039;s no provision for night illumination on the device, but if it was intended for taking only one sight, it could be brought into a lighted area inside the boat or ship where the internal scale could be read.[/QUOTE]</p><p><br /></p>

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