You can see a list of all the countdown latches in your cluster by clicking on the Countdown Latches menu item in the left menu.
A countdown latch has three metrics:
Round: Number of the current round. This number is incremented when the countdown latch reaches 0 and is initialized with a new count.
Count: Initial countdown.
Remaining: Remaining number of expected countdowns.
You can sort the table by clicking on the column headers.