What is the earliest compass in China?

According to ancient mine records, Sina first appeared in Cishan, Hebei Province during the Warring States Period. Sina may be a spoon-shaped thing made of natural magnetite, placed on a smooth plate with directions engraved on it, and identified by the role of a magnet guide. Sina is the ancestor of the compass used now.

Compass is the result of China ancient working people's understanding of magnet magnetism in long-term practice. In ancient China, the compass was first used for rituals, etiquette, military affairs and divination, and to determine the orientation when looking at geomantic omen.

Magnetic meridian circle

Magnetic meridian changes with the seasons. First, on the vernal equinox and autumnal equinox, magnetic meridian coincides with the meridian and meridian of the earth, and the compass points directly to the north and south poles of the earth, with an error of only 0.08 eccentricity of the earth's axis, which can be ignored.

Secondly, in summer solstice and winter solstice, the magnetic meridian and meridian do not coincide, and the magnetic declination is the largest, with the maximum deviation of plus or minus 23.26, that is to say, the magnetic declination near the north and south poles of the earth is the largest. The circumference of the earth divided by the angle of 365 is plus or minus 23, which is equal to the distance between the magnetic deviation point and the north and south poles (plus or minus radian kilometers).