It's an old piece of software buried in my collection from the days when I used to day trade US stocks & pairs. Interestingly, looking back over a rather longer period there appears to be much less correlation between DAX & CAC.
The usual idea with correlations is to find which instruments are highly [un]correlated. You can then trade correlated stocks in the same direction, or take opposite positions in uncorrelated stocks.
For example, if Microsoft and Adobe are highly correlated and Microsoft rises following, say, good earnings you might trade Adobe long expecting it to rise in a similar way. If you bought Microsoft directly you might have missed much of its move. In buying Adobe you hope to benefit from a much larger part of the move when (IF!) it comes.
Vice versa for uncorrelated stocks.