What does the Change field represent on the User Leagues page for SO? Refer to the highlighted areas in the image below:

• Rank: the user's ranking for the selected time period (week, month, quarter, year)
• Change: +/- change representing... ???
• Total Reputation: the user's total reputation
• [Time Period] Reputation: the user's reputation for the selected time period (week, month, quarter, year)

So what is the Change field measuring?