--- Unit.pm	2014-11-03 14:26:42.000000000 +0100
+++ newUnit.pm	2014-11-03 14:26:04.000000000 +0100
@@ -44,13 +44,47 @@
   return $self->{__base_factor};
 }
 
+sub can_convert_to {
+  my ($self, $other_unit) = @_;
+  foreach($self->convertible_units)
+  {
+    my $element = $_;
+    foreach(@$element)
+    {
+      my $subelement = $_;
+      if( $subelement->get_base_name() eq $other_unit->get_base_name() )
+      {
+        return 1;
+      }
+    }
+  }
+  return 0;
+}
+
+sub get_base_name{
+  my $self = shift;
+  my $tmp = $self;
+  while ($tmp->base)
+  {
+     $tmp = $tmp->base;
+  }
+  return $tmp->name;
+}
+
 sub convert_to {
   my ($self, $qty, $other_unit) = @_;
 
   my $my_base_factor    = $self->base_factor       || 1;
   my $other_base_factor = $other_unit->base_factor || 1;
-
-  return $qty * $my_base_factor / $other_base_factor;
+  
+  if($self->can_convert_to($other_unit))
+  {
+    return $qty * $my_base_factor / $other_base_factor;
+  }
+  else
+  {
+    return $qty;
+  }
 }
 
 1;