Oxygen Indicator, USSR, Oxygen Indicator IK-24N (ик-24н)
This is a fine example of a Cold War-era, Soviet, Oxygen System Indicator as used in the USSR Air Force aircraft. The indicator measure and conveys the system oxygen pressure (i.e., quantity) up to 150 kilograms/square centimeter, via the pointer in the upper half of the display. The indicator also provides visual indicator of oxygen flow similar to the WWII-era "blinker" device: as the pilot inhales/exhales, the two white 'eyelids' below center diverge/converge to indicator that oxygen is in fact flowing through the device KP-52M (КП-52M).
The Russian Cyrillic lettering on the instrument, "КИСЛОРОД" means Oxygen, and "МАСЛО ОПАСНО" means Oil, Dangerous. Measures ~2.5 inches diameter and ~4 inches deep.
Many thanks to a colleague in Ukraine for assistance in understanding the device.