You're referring to %M4 on this line:

$M4{$target} = $M4{$target} + $M4_compteur{$target};
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and this one

    $M4{$target} = $M4{$target}/$Duration;
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but declare only $M4, on this line:

  my $M4;
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It appears you are doing the same thing with the variable $M4_compteur.

Try changing

my $M4;
my $M4_compteur;
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to

my %M4;
my %M4_compteur;
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The sigils ($, %, &, *, @) are important. I also find them slightly confusing, as $this, %this, @this, and &this are completely distinct, but the elements of %this and @this are referenced as $this{one} and $this$one. To ease my confusion, I tend to avoid giving scalars, arrays, hashes, and functions names that are the same or too similar.