def to_s(system = :twelve_hour, options = {})
      options  = {use_seconds: true, include_meridiem: true}.merge(options)
      pad = "%02d"
      meridiem = self.meridiem.to_s.upcase
      hour = self.hour(system)
      minute = pad % self.minute
      second = pad % self.second

      string = [hour, minute].join(':')
      if options[:use_seconds]
        string = [string, second].join(':')
      end

      case system
      when :twelve_hour
        options[:include_meridiem] ? [string, meridiem].join(' ') : string
      when :twenty_four_hour
        string
      else
        raise ArgumentError, "system should be :twelve_hour or :twenty_four_hour"
      end
    end
def to_s(system = :twelve_hour, options = {})
      options  = {use_seconds: true, include_meridiem: true}.merge(options)
      pad = "%02d"
      meridiem = self.meridiem.to_s.upcase
      hour = self.hour(system)
      minute = pad % self.minute
      second = pad % self.second

      string = [hour, minute].join(':')
      if options[:use_seconds]
        string = [string, second].join(':')
      end

      case system
      when :twelve_hour
        options[:include_meridiem] ? [string, meridiem].join(' ') : string
      when :twenty_four_hour
        string
      else
        raise ArgumentError, "system should be :twelve_hour or :twenty_four_hour"
      end
    end
Convert {WallClock} to a human-readable format.
 @param [Symbol] system The hour system to use (`:twelve_hour` or `:twenty_four_hour`; default `:twelve_hour`)
 @param [Hash] options Extra options for the string to use
 @option options [Boolean] :use_seconds Whether or not to include seconds in the conversion to a string
 @option options [Boolean] :include_meridian Whether or not to include the meridian for a twelve-hour time
 @example
   time = WallClock.new(5, 37, 41, :pm)
   time.to_s
     => "5:37:41 PM"
   time.to_s(:twenty_four_hour, :use_seconds => true)
     => "17:37:41"
   time.to_s(:twelve_hour, :use_seconds => false, :include_meridiem => false)
     => "5:37"
   time.to_s(:twenty_four_hour, :use_seconds =>false)
     => "17:37"
 @raise ArgumentError Argument isn't a proper system