The Twitter instance user’s follower count history over time, by day, week, and month.
If a notable milestone is within sight, you’ll see a “Next milestone” message which tells you how many weeks it will take to reach that milestone.
Specifically, based on your current rising follower count trend, if you will reach 100, 200, 500, 1k, 5k, 10k, 25k, 50k, 100k, 150k, 200k, 250k, 300k, 500k, 750k, or 1M followers within the next 10 days, weeks, or months, you will see this next milestone message.