Vernier compass


  • Webster's Revised Unabridged Dictionary
    • Vernier compass a surveyor's compass with a vernier for the accurate adjustment of the zero point in accordance with magnetic variation.
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In literature:

They are surveying compasses made of walnut, having maple sighting bars and a silvered brass vernier set under the glass.
"Early American Scientific Instruments and Their Makers" by Silvio A. Bedini