old_contents: """
  Unless otherwise stated, following units are used in this project:
  - length: metre
  - volume: litre
  - temperature: Celsius degree
  - voltage: Volt
  """
  
  # Specify order and name of data columns
  DATA_SPEC = (
      'date',
      'temperature_C',
      'pH',
      'volume_L',
      'nutrients_mL'
  )
  
  PH_ADC_I2C_BUSN = 1
  PH_ADC_I2C_ADDR = 0x4F
  
  PH_ADC_V_REF = 2.5
  PH_ADC_V_OFFSET = 1.251
  
  PH_CALIBRATION = {
      'temperature': 21.2,
      'points': (
          {'ph': 4.0, 'voltage': 1.418},
          {'ph': 7.0, 'voltage': 1.224}
      )
  }
  
  TEMPERATURE_SPI_BUSN = 0
  TEMPERATURE_SPI_DEVN = 0
  
  DISTANCE_GPIO_TRIG = 23
  DISTANCE_GPIO_ECHO = 24
  
  WATER_TANK_CALIBRATION = {
      'points': (
          {'distance': 0.8, 'volume': 0},
          {'distance': 0.5, 'volume': 150},
          {'distance': 0.25, 'volume': 300},
      )
  }
  
  PUMP_GPIO_SLEEP = 17
  PUMP_GPIO_STEP = 27
  
  PUMP_CALIBRATION = {
      'steps_per_litre': 8.4e6
  }
  
  NUTRIENTS_CONCENTRATION_PER_PH = 1.65e-3
  
  MIN_PUMPED_NUTRIENTS = 1e-3
  
  DESIRED_PH = 6.0
  
  SOLUTION_VOLUME = 10
  
  PROPORTIONAL_K = 0.5
  
  CONTROLLER_PERIOD_MINUTES = 5
  
new_contents: """
  Unless otherwise stated, following units are used in this project:
  - length: metre
  - volume: litre
  - temperature: Celsius degree
  - voltage: Volt
  """
  
  # Specify order and name of data columns
  DATA_SPEC = (
      'date',
      'temperature_C',
      'pH',
      'volume_L',
      'nutrients_mL'
  )
  
  PH_ADC_I2C_BUSN = 1
  PH_ADC_I2C_ADDR = 0x4F
  
  PH_ADC_V_REF = 2.5
  PH_ADC_V_OFFSET = 1.251
  
  PH_CALIBRATION = {
      'temperature': 21.2,
      'points': (
          {'ph': 4.0, 'voltage': 1.418},
          {'ph': 7.0, 'voltage': 1.224}
      )
  }
  
  DISTANCE_GPIO_TRIG = 23
  DISTANCE_GPIO_ECHO = 24
  
  WATER_TANK_CALIBRATION = {
      'points': (
          {'distance': 0.8, 'volume': 0},
          {'distance': 0.5, 'volume': 150},
          {'distance': 0.25, 'volume': 300},
      )
  }
  
  PUMP_GPIO_SLEEP = 17
  PUMP_GPIO_STEP = 27
  
  PUMP_CALIBRATION = {
      'steps_per_litre': 8.4e6
  }
  
  NUTRIENTS_CONCENTRATION_PER_PH = 1.65e-3
  
  MIN_PUMPED_NUTRIENTS = 1e-3
  
  DESIRED_PH = 6.0
  
  SOLUTION_VOLUME = 10
  
  PROPORTIONAL_K = 0.5
  
  CONTROLLER_PERIOD_MINUTES = 5
  
subject: remove unused variables