Course Content
Learn Farm Structure and Surveying with Rahul

Variations in Magnetic Declination

Declination is not fixed — it varies with time and location. Variations are classified as:

a) Diurnal Variation

  • Daily variation (~10 minutes) over 24 hours.
  • Greater during daytime.
  • Influenced by: Locality. Season and Time of day

 

b) Annual Variation

  • Yearly change from mean value (~1 to 2 minutes).
  • Depends on geographical location.

 

c) Secular Variation

  • Long-term, irregular variation over decades.
  • Largest in magnitude.

Example: Paris (1680): 11° East, Paris (1820): 22° West

d) Irregular Variation

  • Sudden, unpredictable changes.
  • Caused by earthquakes, solar storms, etc.
Scroll to Top