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Surveyor's Compass

The surveyor's compass, also known as a circumferentor, was one of the primary tools used in land surveying from the 16th through 19th centuries. It combined a magnetic compass with sighting vanes to measure horizontal angles and establish property boundaries.

Key Features

  • Magnetic compass needle mounted in a brass circle
  • Graduated circle divided into 360 degrees
  • Folding sights for taking bearings
  • Level vials for accurate positioning
  • Mounting socket for tripod attachment

Historical Significance

The surveyor's compass was essential in early American land surveys, including the mapping of state boundaries and the Public Land Survey System. Its relative simplicity and reliability made it the standard tool for land surveying until the widespread adoption of the transit in the late 19th century.

{Array.from({length: 72}).map((_, i) => { const angle = i * 5; const length = i % 18 === 0 ? 20 : 10; const x1 = 200 + 155 * Math.cos(angle * Math.PI / 180); const y1 = 200 + 155 * Math.sin(angle * Math.PI / 180); const x2 = 200 + (155 - length) * Math.cos(angle * Math.PI / 180); const y2 = 200 + (155 - length) * Math.sin(angle * Math.PI / 180); const labelX = 200 + 140 * Math.cos(angle * Math.PI / 180); const labelY = 200 + 140 * Math.sin(angle * Math.PI / 180); return ` ${i % 18 === 0 ? `${angle}°` : ''} `; })} N E S W

Interactive Demonstration

Hover over the compass to see how the needle responds to magnetic interference. The compass features precise degree markings and enhanced sighting vanes for accurate bearings.

Using the Surveyor's Compass

Setup

  1. Mount compass on tripod
  2. Level using adjustment screws
  3. Allow needle to settle
  4. Check for local magnetic interference

Taking Bearings

  1. Align sights with target
  2. Read degree marking at needle point
  3. Record bearing in field book
  4. Account for magnetic declination

Maintenance

  1. Keep instrument dry and clean
  2. Check needle pivot regularly
  3. Protect from strong magnets
  4. Store in wooden case