private function addDisplayFields(Fieldset $fieldset)
{
$fieldset->addField('display_pattern', 'text', ['name' => 'display_pattern', 'label' => __('Display pattern'), 'note' => __('A pattern like %s UNIT where %s is the value. Eg : $%s => $20 or %s € => 20 €')]);
$fieldset->addField('display_precision', 'text', ['name' => 'display_precision', 'label' => __('Display Precision'), 'class' => 'validate-digits', 'value' => '0', 'note' => __('The number of digits to use for precision when displaying.')], 'display_pattern');
return $this;
}