Buying an Antique Sextant: A Checklist Before You Bid

Published October 27, 2026 · All guides

A sextant is a classic piece of nautical history and a staple of naval and maritime auctions. It measures the angle between the horizon and a celestial body or landmark. Condition and completeness decide most of the value, so the photos matter.

Know the parts

  • Frame and arc. The graduated scale along the bottom of the frame. It should be clear, undamaged and not corroded.
  • Index arm and micrometer drum or vernier. The index arm swings across the arc, and the drum or vernier gives the fine reading.
  • Index mirror and horizon mirror. The index mirror moves with the arm. The horizon mirror is half-silvered so you can see the horizon through the clear half.
  • Telescope and shades. Tinted filters protect the eye when sighting the sun. Missing shades or a missing telescope lowers value.

Condition checks

  • Mirrors. Look for flaking or missing silvering, cracks and clouding. Replacement mirrors are common, and a seller should say so.
  • Frame and arc. Ask about bends, repairs, solder and heavy corrosion on the scale.
  • Movement. The index arm and drum should move smoothly with no sticking or looseness. Ask if the clamp holds.
  • Original parts. Mismatched screws, shades or telescopes often mean a composite piece.

Maker, markings and case

Look for the maker's name or mark, a serial number, and any retailer's engraving. A fitted wooden case with a maker's or retailer's label adds to value and helps confirm authenticity. Photograph requests should include the arc, the name plate and the case interior.

Spotting reproductions

Decorative reproductions are sold as nautical décor. Warning signs include very light weight, thin lacquered brass with no wear, blurred or machine-perfect engraving, and mirrors that are plain glass with no silvering. If the price seems low for an antique with a case, ask for more photos.

Display vs. navigation. Treat an antique sextant as a collectible. If you intend to use one for navigation, have it inspected by a qualified instrument technician, and don't rely on it without checking its accuracy.

Auction habits that help

  • Set your maximum before the final minutes and stick to it.
  • Add shipping and insurance, since brass instruments and cases are heavy and fragile.
  • Ask about provenance, including where it was used or found.
  • Compare ended listings for similar makers to see where the market sits.

Where to browse

See antique sextants, marine chronometers, or brass compasses, and sort by ending soonest. Head back to the NavalBids home page for more categories.

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