code: func (m *Meter) Add(size int64) {
  	if m == nil {
  		return
  	}
  
  	defer m.update(false)
  	atomic.AddInt32(&m.estimatedFiles, 1)
  	atomic.AddInt64(&m.estimatedBytes, size)
  }
docs: // Add tells the progress meter that a single file of the given size will
  // possibly be transferred. If a file doesn't need to be transferred for some
  // reason, be sure to call Skip(int64) with the same size.