Carrot is an extension for Codeforces, a free, public challenge site. It displays the standings of active and completed contests. It can also be used to enhance Codeforces ranklists. 

How does Carrot calculate delta?

We calculate deltas based on the current standings of a contest. Carrot does this in real-time, so the calculation occurs as soon as the ranklist is opened. In addition, Carrot also adds a column showing the delta required to rank up.

It is useful for an active contest:

In an active contest, we calculate deltas in real-time.

It is useful for a finished contest:

In a finished contest, we calculate the deltas at the end of each contestant's run.