In Judo, improvement and understanding of the art is denoted by a system of rankings split into kyū and dan grades. These are indicated with various systems of coloured belts, with the black belt indicating a practitioner who has attained a certain level of competence. The Kōdōkan Kyū-Dan ranking system are ranked according to their skill and knowledge, and, for later dan grades, their contribution to the art. Their rank is indicated by the colour of belt that they wear. There are two broad categories of rank: those who have attained a level of competency at which they are considered worthy of a and who hold grades and those who are yet to attain that level and who hold grades. Those who hold dan grades are collectively termed (literally "person who has dan") and those with kyū grades are , literally "person without dan". This ranking system was introduced by Kanō Jigorō, the founder of judo, in 1883. However, the current system is not the original one, but based on Kanō's last system introduced between 1926-1931, with some modification shortly after Kanō's death in 1938. The first dan grades were awarded to his students Saigō Shirō and Tomita Tsunejirō. Since then it has been widely adopted by other modern martial arts. In the current system as in use in Japan, there are six student grades ranked in descending numerical order. Beginners were given the rank of and wore a light blue belt. Once they had passed an elementary level of instruction, they were promoted to , when they would adopt the white belt. This they wore through . The remaining three grades (, and were all indicated with brown belts (for seniors) or with purple belts (for juniors). 1st kyū is the last kyū rank before promotion to first degree black belt (shodan). There are (in practice) 10 dan ranks, which are ranked in ascending numerical order. Highest ranking jūdōka Kōdōkan-graded jūdan holders The ninth (kudan) and tenth degree black belt (jūdan) and, theoretically, those higher, have no formal requirements. Only 15 individuals have been promoted to the rank of Kōdōkan 10th dan. On January 6, 2006, three individuals were promoted to this rank simultaneously: Daigo Toshirō, Ichirō Abe, and Ōsawa Yoshimi. This is the most ever at the same time, and the first in 22 years. No one has ever been promoted to a rank higher than 10th dan,