Can you explain Chess Ratings to me?

Elo is the name of the man who made the mathematical / statistical system of rating one opponent against another, There are others. This system is used in other one on one competitions.

Everyone starts off with a base rating of '1100'. Then after playing a number of games this number will increase to reflect probability of win loss or draw. Two opponents with the same rating would have a 50 / 50 chance of winning or losing. A difference of 100 points would see the % change.

A national or world rating, involves real players, in real competitions, and therefore is the only real measurement of skill and achievement. However I am surprised that the CM has such a difference. But then again, I am surprised an unrated player gets 1613 on their first tournament. Congratulations.

Edit: It has been pointed out to me, that in the USCF rating system initial 'high' ratings are not unusual. [Thanks to The Green Bishop] And that the method I described, where I am, is not the same as the USCF one. I am checking my facts.

Edit: This is a good question as I had assumed that everyone used the same exact rating system.

From Wikipedia------------------

Elo ratings of these various organizations are not always directly comparable. For example, someone with a FIDE rating of 2500 will generally have a USCF rating near 2600 and an ICC [internet chess club] rating in the range of 2500 to 3100.

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Subsequent statistical tests have shown that chess performance is almost certainly not normally distributed. Weaker players have significantly greater winning chances than Elo's model predicts. Therefore, both the USCF and FIDE have switched to formulas based on the logistic distribution. However, in deference to Elo's contribution, both organizations are still commonly said to use "the Elo system".

http://en.wikipedia.org/wiki/Elo_rating_system#Imp...