code: func (d *ADS1x15Driver) ReadDifference(diff int, gain int, dataRate int) (value float64, err error) {
  	if err = d.checkChannel(diff); err != nil {
  		return
  	}
  
  	return d.rawRead(diff, gain, dataRate)
  }
docs: // ReadDifference reads the difference in V between 2 inputs.
  // diff can be:
  // * 0: Channel 0 - channel 1
  // * 1: Channel 0 - channel 3
  // * 2: Channel 1 - channel 3
  // * 3: Channel 2 - channel 3