The metric divides compression ratio by log compression time. (Ignore for now the normalization to a standard compressor.) This is: r / log(T) That does

The metric divides compression ratio by log compression time. (Ignore for now the normalization to a standard compressor.) This is: r / log(T) That doesn't seem like a good metric, because it overvalues changes in T. For example, say we currently can manage 10% compression (ratio = 100/90 = 1.11) and it takes us 16ms. That's r / logT = 1.11 / log(16) = 0.2775 Now we have two proposals. One brings us to from 10% compression to 55% compression (ratio = 100/45 = 2.22) while the other one drops compression time to 4ms: r / logT = 2.22 / log(16) = 0.555 r / logT = 1.11 / log( 4) = 0.555 But improving compression by 5x matters more than improving speed by 4x. Take this to the extreme: a compressor that exits immediately leaving its input unchanged has the best possible score here, despite being useless.