var digit_length=0;
function TabNext(obj,event,len,next_field) {
	if (event == "down") {
		digit_length=obj.value.length;
	}
	else if (event == "up") {
		if (obj.value.length != digit_length) {
			digit_length=obj.value.length;
			if (digit_length == len) {
				this.document.getElementById(next_field).focus()
			}
		}
	}
}