I have an essentially similar one, though without I try and find it I can't recall its make. I bought it quite recently, brand-new, too – within the last decade anyway, for use in my hobby of geology… but have never used it!
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I've also owned a "pair" of Suunto (Finnish-made) clinometer and compass, each reading to half a degree. They each fit a small aluminium-alloy block of identical external dimensions and bores, maybe 70 X 40 X 12mm outside.
The clinometer uses a weighted protractor, the compass is magnetic; both are read by sighting past the index mark with one eye while reading the scale through a lens built into the body.
Though of pocket-size they are on lanyards threaded through small leather pouches so they can be carried slung round the neck, for ready use.
I do not know Suunto's history and original main market, but these instruments were once used extensively for surveying (mapping) caves to high grade, though more often now this is done by a type of laser range-finder and the data then fed into a plotting programme.
I bought mine from a second-hand market near Glasgow, and when I cleaned them discovered they bore vibrator-engraver markings of University of Hull Geology Department. I haven't the foggiest idea how they ended up where they did; but they were labelled with rather vague ideas of "some sort of compass". I explained them to the staff, who obligingly wrote new labels for them. Ten minutes later I went back and bought them!. I no longer have them, but donated them to one of my caving-clubs.