def setup_year_and_month(new_year, new_month)
      if new_month > 12 || new_month < -12 || new_month == 0
        raise Exception "Month out of range.  Allowable values: 1..12 and -12..-1."
      elsif new_month < 0
        @year = new_year - 1
        @month = 13 + new_month
      else
        @year = new_year
        @month = new_month
      end
    end
def setup_year_and_month(new_year, new_month)
      if new_month > 12 || new_month < -12 || new_month == 0
        raise Exception "Month out of range.  Allowable values: 1..12 and -12..-1."
      elsif new_month < 0
        @year = new_year - 1
        @month = 13 + new_month
      else
        @year = new_year
        @month = new_month
      end
    end
if month > 12 or < -12 or == 0, raise exception
 if the month < 0, then subtract that number from 12 and decrement the year
 otherwise, just set the month and year

 @param [Fixnum] new_year
 @param [Fixnum] new_month