I am not able to understand what is pendulous suspension and how centre of gravity and centre of suspension are related in magnets and their errors. Can someone explain this in layman language or could share the link which gives good 3d animation of the same.
This video covers it pretty simply. The compass magnets are attached to the bottom of an upside down cone, which is resting on a spike. The weight of the compass magnets, and the center of gravity of the assembly as a result, is near the bottom of the cone and the "hang point" is up near the top at the tip of the spike.
It's a cone pendulum; basically a lady in a hoop skirt, out on the dance floor (put a couple of bar magnets alongside at at the bottom of the skirt, stick her in a vat of kerosene to dampen the skirt's movements, and there's your compass-lady).
The pendulum arrangement keeps the compass magnets more or less level to the earth even if the spike it's on is tilted (mostly to accommodate changes in pitch attitude with speed and stabilized climbs and descents), within the range of movement of the cone. Compass units in ships (and very early aircraft compasses) achieve this by having the compass float on water (or some other fluid) within the housing so the compass can stay horizontal while the ship pitches and rolls.
The various turning errors relate to how the pendulum reacts to accelerations and apparent gravity (think of the lady's hoop skirt tilting off vertical as she starts to move, for example), the C of G of the cone being below the hang point, while at the same time having the magnetic alignment forces acting on the magnets. The result is readings that wander in specific directions (acceleration/deceleration and turning errors) if there are any lateral accelerations going on, and while the magnets are rotating, because of the "struggle" going on between the magnetic forces and the inertial forces. The compass reading is only valid when the inertial forces have gone away, when there is a steady state condition of no turns and constant speed.