Making a compass is the best breakthrough in the world. With a compass, you can know the direction of the compass, right? A compass that works well, will always head north. The north in question is the north of the magnetic field. If you want to find a direction opposite the north, you only need to see where the north is and look at the direction of the magnetic needle that is opposite the north. That's where you will find the answer.
When you use a compass, of course, there is a point in the middle of the compass that sometimes each compass is different right? There are compasses that make it with detailed directions, there are those that make it only with 4 cardinal directions namely north, south, west, and east. With different designs, but the definition, function, and also the name remains the same. Namely, the compass rose. Because the shape of the magnetic needle is like a sharp rose. The compass rose is known by several similar names namely the wind rose or wind of the rose. Not too different right? But the more innovations there are rose compass is sometimes made in a unique form. Maybe you can find the latest reference from the compass on the internet.
0 degrees is a validation of true north. If you want to find the accuracy of a cardinal direction, the method of seeing the magnetic needle at 0 degrees is a good way. Because North = 0 degrees. If you use a compass made with detailed angles on the circle, North will be at a 360-degree angle to a full circle. If the North magnetic needle is not at 0 degrees, it is certain that the compass you have is damaged so it cannot show the right direction.
Almost all mobile phones have a compass feature in it. There is a default application, there is also a feature of an application for example Maps. However, some mobile phones in ancient times did not yet have a compass feature. Compass features on the phone usually depend on the specifications of the phone. If you don't have a spare part that can support the magnetometer in it, of course you can't expect a compass inside. You can only have a compass if it's separate from the phone.