What are the Earth's magnetic elements? Define them and list them.

(N/A) To completely describe the Earth's magnetic field at any point on its surface,three physical quantities are required,which are known as the magnetic elements of the Earth. These are:
$(1)$ Magnetic Declination $(D)$: The angle between the geographic meridian and the magnetic meridian at a place.
$(2)$ Magnetic Inclination or Dip Angle $(I)$: The angle that the total magnetic field vector of the Earth makes with the surface of the Earth (horizontal) in the magnetic meridian.
$(3)$ Horizontal Component of Earth's Magnetic Field $(H_E)$: The component of the Earth's total magnetic field vector in the horizontal direction in the magnetic meridian. It is related to the total field $B_E$ and dip angle $I$ by $H_E = B_E \cos(I)$.