code: function checksum$4(data) {
  	var result = 0;
  
  	for (var i = 0; i < 13; i++) {
  		result += parseInt(data[i]) * (3 - i % 2 * 2);
  	}
  
  	return Math.ceil(result / 10) * 10 - result;
  }
docs: Calulate the checksum digit