private int placeOfLastMathSign()
	{
		String expressionInDisplay = getDisplay().getText();
		int lengthOfExpression = expressionInDisplay.length();

		while (lengthOfExpression > 0)
		{
			String lastCharacter = expressionInDisplay.substring(lengthOfExpression - 1,
					lengthOfExpression);
			if (lastCharacter.equals("*") || lastCharacter.equals("/") || lastCharacter.equals("+")
					|| lastCharacter.equals("-") || lastCharacter.equals("^"))
			{
				return lengthOfExpression;
			}

			lengthOfExpression--;
		}

		return lengthOfExpression;
	}