The corrector gives you an evaluation for every job you submit. Your current rating is an average of the last 25 evaluations you received for the jobs you submitted.

When the corrector decides whether the job goes back to you for reworking he has to include this evaluation and comment listing the improvements that need to be made.

You can follow why your rating has changed based on the comments in your work history. However, this only represents the momentary situation. A short time later, positive evaluations can increase your rating or negative evaluations can make it drop.