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For a given bank angle, turning errors on a direct reading compass are:
  • A
    greatest on east/west headings, and are least at high latitudes.
  • B
    greatest on north/south headings, and are least at high latitudes.
  • C
    greatest on north/south headings and at high latitudes.
  • D
    greatest on east/west headings and at high latitudes.
Turning errors are greater on North/South headings and at high latitudes as they are directly related to the vertical component of the magnetic field of the Earth. The higher the dip angle induced by the vertical component (so at high latitudes), the larger the turning errors.
An easy way to remember the turning errors is by using the acronym ‘UNOS’:
  • UN – Undershoot = apparent turn to the North.
  • OS – Overshoot = apparent turn to the South.

Note: ‘Undershooting’ means turning through a smaller angle and should not be confused with ‘under-reading’ which means the heading indicated on the scale is too small.

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