The Earth’s magnetic field does not flow evenly between the magnetic poles along the surface of the planet. Rather the magnetic field lines tilt into the ground increasingly as you approach a pole. At the magnetic poles, the field lines are completely vertical, flowing perpendicular to the surface.
To learn more about the behavior of the earth magnetic field a good place to visit is the National Geophysical Data Center website of the NOAA.
Any practical magnetic compass must show the horizontal component of the local magnetic field line to be precise. To accomplish this without having to manually compensate for the natural tilt in the magnetic lines, compass manufacturers usually use the weight of the needle or card to account for the vertical component of the magnetic field. This is referred to as magnetic zone balancing.
Suunto mechanical compasses have two balancing solutions: one is a two-zone system with a northern hemisphere zone and a southern hemisphere zone (with zones overlapping several degrees). The other is a single global system with one needle balanced to work anywhere on Earth.
The two-zone system uses a weighting method that adds mass both to the end of the needle that would rise due to the magnetic field inclination and to the needle assembly that must move as well to compensate for the tilt and pivot motions.
Suunto has created a delicate compromise between these two balancing weights that minimizes sway and self-rotation of the needle. This compromise has allowed Suunto to create a solution requiring only two balancing zones. In the past, four or five zones were required for accurate balancing.
Suunto’s globally balanced needles use a construction where the needle and the magnet tilt independently of each other. This allows the needle to stay parallel with the compass capsule while the magnet tilts with the vertical component of the earth magnetic field without pulling down the needle. And yet when the magnet turns due to the horizontal component of the magnetic field, it pulls the needle along with it to show magnetic North.
This unique construction also allows the compass to work even when tilted up to approximately 20 degrees. The needle is more stable even when you are moving and settles faster when you stop, making globally balanced Suunto compasses fantastic to use.