public function usingReference($reference, $description)
    {
        $this->reference   = $reference;
        $this->description = $description;

        return $this;
    }
public function usingReference($reference, $description)
    {
        $this->reference   = $reference;
        $this->description = $description;

        return $this;
    }
public function usingReference ( $ reference , $ description ) { $ this -> reference = $ reference ; $ this -> description = $ description ; return $ this ; }
Set the product reference number to bill the account.

@param int    $reference
@param string $description

@return self
Set the product reference number to bill the account .