function luhnCheckDigit(mynum)
{
	var sum = 0;
	var validChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVYWXZ_";
	mynum = mynum.toUpperCase().replace(/^\s+|\s+$/g, '');
	
	for (var i = 0; i < mynum.length; i++)
	{
		var ch = mynum.charAt(mynum.length - i - 1);
		if (validChars.indexOf(ch) < 0)
		{
			WScript.echo("Invalid character(s) found!");
			return false;
		}
		
		var digit = ch.charCodeAt(0) - 48;
		var weight;
		
		if (i % 2 == 0)
			weight = (2 * digit) - parseInt(digit / 5) * 9;
		else
			weight = digit;
		
		sum += weight;
	}
	sum = Math.abs(sum) + 10;
	var digit = (10 - (sum % 10)) % 10;
	
	return digit;
}