There are so many different rating organizations, and the levels usually don't translate exactly from one to another. There are European, Chinese, Korean, Taiwanese, and Japanese rating organizations, plus all of the internet go sites like IGS, KGS, etc. Someone who is 2 dan on one system might only be 2 gup/kyu on another - so it is all very approximate. Plus, there are many others who play who don't have a ranking from ANY system, and often they just guess how strong they are, based on how well they do against other players of a known rank.

This site uses an arbitrary number/color system based purely on the results of games played on this site. However, many players manipulate their ranks to get an either artificially high or low number. This is done easily - there are some players who will only play against beginners - so they win every game they play and get a high number, even though they have a low level of go skill. Others have learned how to "cheat" by playing to win by using the time limit, rather than skill. Another player might deliberately lose games in order to keep the rank artificially low. So while sometimes there is a correlation between one's numerical rank and go skill, it is not always the case.