Percentage faster/slower
From wikinotes
percentage faster/increase
(new - old) / old * 100 # how much faster is 'new' than old
percentage slower/decrease
(old - new) / old * 100 # how much slower is 'new' than old
(new - old) / old * 100 # how much faster is 'new' than old
(old - new) / old * 100 # how much slower is 'new' than old
