From Wiki

Фабрика Счётних Приборов Artillery Rule

• Type: Closed Body Trig Artillery
• Size: 11 Inches / 27 cm
• Material: Ash and celluloid
• Scales:
  • Front: 1:50000 1:25000 \ β N2 [ S ST T N ] N lgN | cm
  • Back: [ S ST T N ]

From the "Slide Rule Factory" in Leningrad. This is essentially a trig rule that is calibrated in Russian mils, 1/6000 of a circle. Flip the slide over to the red side to work in degrees. A conversion scale from mils to degrees is under the slide. All the math you need to know is on the back, and centimeter, 1/25000 and 1/50000 scales are provided for reading maps.

The β scale does WHAT?

In black paperboard case.