Grig:

Ah, I made a mistake in the subroutine. It was:

sub get_bin {
   # Determine the name of the bin to put the value into
   my $val = shift;
   my $bin_min = int($val / 10);
   my $bin_max = $bin_min + 10;
   return "$bin_min-$bin_max";
}
[download]

but it should have been (untested):

sub get_bin {
   # Determine the name of the bin to put the value into
   my $val = shift;
   my $bin_min = 10*int($val / 10);
   my $bin_max = $bin_min + 10;
   return "$bin_min-$bin_max";
}
[download]

I forgot the "10*" when computing $bin_min, so instead of 0, 10, 20, etc., it was using 0, 1, 2, ...

...roboticus