In this case the corelation between the numbers is very obvious. We generate
random integers in the range [0, 255], which results in 
possible
pairs corresponding to crosses on the plot. But we get only 127 pairs
(if I counted correctly).
Figure 1: A graph of the correlations test
for the simple random number generators
In this case the distribution of pairs is less organized. There are
clusters of them in some parts and open spaces in other. In other words, the
pairs are distributed more randomly.
Figure 2: The result of the same test for the
random number generator drand48 which is part of
the AIX system.