Test plot
                                                                                              y2
  10 ++---------+----------+---------+----------+----------+----------+---------+---------** 30
     +          +          +         +          +          +          +      data 0 ****** +
     |                                                                               ***   |
     |                                                                            ***      |
   9 ++                                                                         **         |
     |                                                                       ***          +G 25
     |                                                                    ***              |
     |                                                                  **                 |
   8 ++                                                              ***                   |
     |                                                            ***                      |
     |                                                          **                         |
     |                                                       ***                          ++ 20
   7 ++                                                   ***                              |
     |                                                 ***                                 |
     |                                               **                                    |
     |                                            ***                 G                    |
   6 ++                                        ***                                        ++ 15
     |                                       **                                            |
     |                                     **                                              |
     |                                  ***                                                |
     |                                **                                                   |
   5 ++                             **                                                     |
     |                           ***                                                      ++ 10
     |                         **               G                                          |
     |                       **                                                            |
   4 ++                   ***                                                              |
     |                 ***                                                                 |
     |               **                                                                   ++ 5
     |            ***                                                                      |
   3 ++        ***         G                                                               |
     |      ***                                                                            |
     |    **                                                                               |
     G ***      +          +         +          +          +          +         +          +
   2 **---------+----------+---------+----------+----------+----------+---------+---------++ 0
     1         1.5         2        2.5         3         3.5         4        4.5         5
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