private DIGIT handleZERO(double d) {
		DIGIT digit = DIGIT.ZERO;

		if (d == 0.0) {
			operandValue *= 10;
			digit = DIGIT.ZERO;
		} else if (units.contains(d)) {
			operandValue *= 10;
			operandValue += d;
			digit = DIGIT.UNITS;
		} else {
			System.out.println("NLCalc does not understand the input: Only zeros and units accepted after a zero");
			System.out.println("Please try again.");
			System.exit(1);
		}

		return digit;
	}