My google fu is weak.

In Golden Cheetah if I go to Trends > Summary and look at the Athlete Bests I see 30 Sec peak power, 1 min peak power, etc. In each of those sections I see the position number, wattage, date and a number in parenthesis. What is that number telling me and why is it something negative and other times positive?

Example below.

Thanks

20 min Peak Power

1. 258 7 Apr 2019 (-2)
2. 242 10 Aug 2019 (-7)
3. 242 8 Aug 2019 (-9)
4. 238 23 Apr 2019 (10)
5. 236 21 Apr 2019 (13)
6. 235 21 Mar 2019 (-5)
7. 233 28 Aug 2019 (-6)
8. 233 11 Oct 2019 (9)
9. 233 13 Aug 2019 (-8)
10. 232 17 Oct 2019 (-3)