An isogonic line along which there is no magnetic variation is called what?

• A. Airfoil
• B. Air Density
• C. Agonic Line
• D. Altimeter

Answer: (C)

Magnetic variation, or declination, is the angle between true north and magnetic north. Lines where the variation is the same are called isogonic lines. Along the agonic line the magnetic variation is zero, so magnetic north and true north align and a compass would point toward true headings rather than magnetic. This is why the term for an isogonic line with zero variation is agonic.

The other options don’t relate to magnetic variation: an airfoil is a wing shape, air density describes how much matter is in the air at a location, and an altimeter measures altitude.