Magnetic declination or variation is the angle on the horizontal plane between magnetic north (the direction the north end of acompass needle points, corresponding to the direction of the Earth'smagnetic field lines) and true north (the direction along a meridian towards the geographic North Pole).
u just need to calculate it by taking the ratio, there is no other way to calculate it .
place your compass in the magnetic horizontal plane and then measure the angle .
HERE U ARE NOT USING ANY PREVIOUS DATA .
HOPE U UNDERSTAND ,
ANY DIFFICULTY , LET ME KNOW ..
