No argument in conversion methods

temperature_conversions.rb

class UnitConversion
  def initialize(measurement, unit)
    @measurement = measurement
    @unit = unit
  end
  
  # Proxy with Kelvin
  def to_kelvin
    case @unit
    when 'celcius'
      @measurement += 273.15
    when 'rankine'
      @measurement /= 1.8
    when 'fahrenheit'
      @measurement = (@measurement + 459.67) * 5 / 9
    end
  end

  def to_celcius
    case @unit
    when 'kelvin'
      @measurement -= 273.15
    when 'fahrenheit'
      self.to_kelvin
      @unit = 'kelvin'
      self.to_celcius
    end
  end
end