The shifted geometric mean SGM of the n nonnegative numbers v[1],...v[n] is

    SGM = exp(sum{i in 1..n} ln(max(1,v[i]+sh))/n) - sh, sh nonnegative

In our benchmarks, where the v[i] are Wallclock seconds, we use sh = 10.

Then we scale the means by dividing them by the smallest mean.