if (('' eq ref $conv_units) && ($conv_units =~ /convertible/)) {
$conv_units = AM->convertible_units($all_units, $part_unit_name, $conv_units eq 'convertible_not_smaller');
if (('' eq ref $conv_units) && ($conv_units =~ /convertible/)) {
$conv_units = AM->convertible_units($all_units, $part_unit_name, $conv_units eq 'convertible_not_smaller');