Assuming (as we must -- else your problem has no clean solution) that the elements in @data are unique.

Given:

my @data    = ('70.1', '75.3','76.5', '87.4');
my @numbers = ('0.001','0.34','0.456','0.521');
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...then just do:

my %look_up;
@look_up{@data} = @numbers;
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...and then you can retrieve the values as needed. E.g.: print $look_up{76.5}, "\n";   # prints: 0.456

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"Perl is a mess and that's good because the
problem space is also a mess." - Larry Wall