Powergain determines how much power the ranker gains per second.
The formula for calculating powergain is (ladder_position - 1 + bias) * multi, where
1. ladder_position - your current position on the ladder;
2. bias - your current bias count;
3. multi - your current multi count.
At top-1 position powergain always equals 0.

On the screenshot we can see that the current ladder_position of a ranker equals 112, bias_count equals 3 and multi_count equals 2.
Calculating with the given formula returns (112 - 1 + 3) * 2 = 114 * 2 = 228 power per second.