Sovjet slide rule with small pins near the end of the slide.

Data:

• On left under and right upper side of the slide a very small steel pin of about 1 mm length and 1 mm diameter is present. It prevents the slide to slip out of the main body at the end of the left or right side. For that purpose the groove in the main body is less deep over the last 1 cm. The difference in depth is comparable to the pin length. On the photo the jump is visible near the dark shade (caused by the artificial lamp light). The final photo shows the final position of the slide.
• This slide is also available in the excellent database of the Slide Rule Museum:
  Soviet-LFAI Aviation Navigator's
  REF S531
  Made in USSR
  Scales: The Corrected height
  Height and speed on the device
  Distance
  Radiuses of a turn - distances – heights
  Otdel Mectnoi Promezhlennocti Lengoricpolkoma
  Fabrika Schetnex Priborob, Leningrad
  Department of Local Industry of Leningrad Municipal Executive Committee
  Plant of computational instruments, Leningrad.
• It seems that this sliderule is produced in Leningrad.

Questions:

1. I am not an aviation engineer and have no idea about the use of the scales.
   Can somebody translate it to English and explain the scales and the use of it?
   Automatic translation of the images: Russian English
   This slide rule is mentioned on sliderule@groups.io
   
2. But my real question is about the 2 pins.
   1. I have never seen it before. Are other (aviation?) sliderules known with such pins or comparable stops?
   2. This is an aviation sliderule. Are the pins intended to prevent losing the slide in a cockpit? I can imagine that the pilot is busy with other work than searching for a lost slide.
3. The slide stops indeed at the end of the body. Due to the tolerances in the main body the slide can be removed. Was that the intention during production? Has anybody an idea how that was foreseen?