I asked this question on the forum, and came to the conclusion that performance would be calculated using the following formula:
1 - lower/higher * 100
Based on that, between 0.246 and 0.321, would the performance be increased by 23%?
Thanks.
If the original value of a measurement is $0.246$ and the new value is $0.321$ you calculate the relative change by dividing: $$ \frac{\text{new}}{\text{old}} = \frac{0.321}{0.246} = 1.30 . $$ That corresponds to a $30\%$ increase, because you can rewrite the equation as $$ {\text{new}} = 1.30 \times{\text{old}} = 1 \times {\text{old}} + 0.30 \times {\text{old}} . $$
The logic has nothing to do with whether the measurement went up or down. You don't always divide the smaller number by the larger. If the change was from $5$ to $4$ the calculation is $$ \frac{\text{new}}{\text{old}} = \frac{4}{5} = 0.8 = 1 - 0.2 $$ which corresponds to a $20\%$ decrease.