private boolean checkValidSubstraction(char c1, char c2) {
        if ((c1 != 'I') && (c1 != 'X') && (c1 != 'C') && (c1 != 'M')) {
            showCannotSubstractMessage(c1, c2);
        }
        float value1 = getValue(c1);
        float value2 = getValue(c2);

        if ((value2 / value1) > 10) {
            statusCode = 2;
            return false;
        }
        return true;
    }