module Format360N # => (-179..180)
  def time
    (v = super) > 180 ? v - 360 : v
  end

  def time=(arg)
    super arg % 360
  end
end

module Format24P # => (0..24)
  def time=(arg)
    super arg % 24
  end
end

class Clock
  attr_accessor :time

  def initialize(format = nil)
    @time = 0
    format ||= Format24P
    self.extend format
  end
end

# c = Clock.new Format360N
# c.time += 170
# c.time += 35 => -155