Nestler Flugzeit military airplane slide rule 1940 Germany

This is a military slide rule used for pilots and army purposes around the second world war. It is meant for reconnaissance purposes determining airplane speed and or the time it will take to get closer or further from a target. It comes in the original black cardboard case with Nestler stamp. but has a small part of the blak paper cover missing, the cardboard inner holder is complete with clear signs of storage. I am guestimating this rare rule is from ca. 1940. Everything is complete, no cracks, chips or dings and in working condition with noticeable signs of use and age, mostly to the cursor chromium plated edges. It measures 29,5 cm or 11 3/4 inches wide. Check the attached video on how to work your vintage man tool : slide rule operation instructions! And also make sure to take a quick look at the 55cm / 22″ flugzeit I sold before.