This is a Russian Soviet ZMD model M-19 hair hygrometer which I believe was made in 1981.  Unusual for its open construction, it works very well.  Specially treated human hair is used as the humidity sensor.  It has a thumb wheel at the top which may be turned for calibration.  Previously this design was manufactured as model MB-1.  The catalog says it's accurate to +/-1%.  It must be vertical for it to operate.  The hair element is very thin and looks fragile.  The single strand of hair is not obvious in the photo. It's approximately 11 inches tall and the scale is about 5.25 inches wide.

Go to Soviet instrument catalog page.

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