It automatically calculates the total number of green card applicants (both AOS and CP) waiting ahead of you.
A graph is generated to not only show your current place in line but also your progress over the past two years.
For example, you may still see pending cases ahead of you even if your I-485 has been approved.
Once those numbers of green cards are given out, then there are no more available that year. In the end, you could be waiting as little as a few months to adjust status, or you could be waiting in line for years.
To check your position in the green card queue, select your case information and click "Track Green Card": Note that although USCIS generally operates on a first in first out (FIFO) basis, there are many factors affecting case processing.