More than 300 horse breeds have been found in the world. Like the human society, according to the different skin color, can be divided into yellow, white, black and brown people, in the horse world, in the history of equestrian sports is the longest and the most developed Europe, from the horse lineage and nerve type, can be divided into hot-blooded horse, cold-blooded horse and warm-blooded horse.

As the saying goes, "a man has size, a horse has height."Therefore, it is very important to measure the height of horses, especially in horse registration, horse trading and other occasions. Most countries of the European-dominated world use cm as the standard unit of measurement. However, in the United Kingdom, the United States, Canada, Australia and other countries still have the habit of using "palm width" (hereinafter referred to as "palm"), in many horse books, magazines, newspapers using "palm width" is still high frequency. In practical applications, people in English countries often misunderstand this concept. So it is necessary to say it here.