Rating System

I’ve created my account on CodeChef last week. Then I participated in Cook-off and before this contest my rating was 0. After one day, my rating was updated to 1477 but under the CodeChef rating, it is showing that my highest rating is 1500. I don’t know when was my rating 1500. Can anyone explain? Here, are some screenshots.

Your initial rating is taken as 1500 for calculation but shown as 0 before your first contest.