What is magnetic declination ?

The total intensity of earth's magnetic field at the magnetic equator is $5$ $units$. Its value at a magnetic latitude of $37^o $ is equal to 

A telephone cable at a place has four long straight horizontal wires carrying a current of $1.0\; A$ in the same direction east to west. The earth's magnetic field at the place is $0.39 \;G ,$ and the angle of dip is $35^{\circ} .$ The magnetic declination is nearly zero. What are the resultant magnetic fields at points $4.0\; cm$ below and above the cable?

The vertical component of the earth's magnetic field is $6 \times 10^{-5} T$ at any place where the angle of dip is $37^{\circ}$. The earth's resultant magnetic field at that place will be $\left(\right.$ Given $\left.\tan 37^{\circ}=\frac{3}{4}\right)$

Angle of dip at a place is $30^o,$ and the horizontal component of earth's field is $5 \times 10^{-5}$ $tesla$, then the vertical component and the total magnetic field at that place is :-

The angle between the magnetic meridian and geographical meridian is called