Performance Index Benchmark

I suppose this is curiosity more than anything, but I was wondering if anyone knew the specifics of how the Performance Index is benchmarked. Obviously, they say it's 50% time-based, etc... but the values of each are still uneven, and you didn't want a CPU to have a higher score if it has a higher value for the time-based benchmarks. So I was wondering if anyone knew how I might be able to calculate it if I had the benchmarks in front of me and a calculator...