LESSON 26

• COMPASS is a handheld instrument for determining horizontal direction of a line with reference to the magnetic meridian
• ESSENTIAL FEATURES OF A COMPASS:

  Compass Box

  Line of Sight

  Magnetic Needle
• TYPES OF COMPASSES

  BRUNTON

  LENSATIC

  SURVEYOR'S

  PLAIN POCKET

  PRISMATIC

  FORESTER'S

  TRANSIT
• BRUNTON COMPASS -most versatile and widely used compass - it combines the main features of prismatic compass, sighting compass, hand level and clinometer.

  -for preliminary and exploratory surveys, engineering type surveys, and topographic surveys
• LENSATIC COMPASS - compass designed for military use
• SURVEYOR'S COMPASS - popularly used earlier for running limited plane surveys of reasonable accuracy. - it is now used for forest surveys, in retracing old land surveys, and in geological explorations.
• PLAIN POCKET COMPASS -similar to surveyor's compass except is has no sight vanes

  -It used for reconnaissance and exploratory surveys
• PRISMATIC COMPASS -have been widely used by sailors for navigation at sea, liquid compasses
• TRANSIT COMPASS is often used to check horizontal angles and directions measured or laid off during transit surveys.
• MAGNETIC DECLINATION is the horizontal angle and direction by which the needle of a compass deflects from the true meridian at any particular locality