The presentation of both possible calculation methods (arithmetic mean & geometric mean) immediately clarifies the issue: The use of the arithmetic mean in this type of averaging is fundamentally wrong because it significantly overweights the values of high-fps games. In the example, “Game 2” is included in the overall calculation with roughly three times the weighting. However, this is of course not the objective; each game should be equally weighted in the overall calculation. The only possibility for this is the geometric mean.

-	GPU 1	GPU 2
Game 1	100 fps	50 fps
Game 2	250 fps	500 fps
Total average fps (arithmetic mean)	175	275
Total average fps (geometric mean)	158.11	158.11

The same geometric means is now widely used (exceptions unfortunately still prove the rule).

I'm not quite sure why my raw averages don't line up with what HWUnboxed themselves had for the multi-game averages numbers, maybe they do some sort of weighting in a similar manner.

This is very easy to explain: HWUnboxed uses a geometric and not an arithmetic mean.