I use Arena for tournaments between chess engines.
The interesting thing is that in different 64-bit multi-processor computers ranking is slightly different. I was expecting that they should be the same.
Do you have any idea why this happens?
As an example Booot 6.2 64-bit loses most of the games on a low end new PC. However in a stronger PC with newer 'Core i7' CPU it can even have the same score as Stockfish 8 (which most of the time is in top of tables).