code: func (b *SparkChart) AddData(val float64) {
  	b.mtx.Lock()
  	defer b.mtx.Unlock()
  
  	b.data = append(b.data, val)
  
  	_, width := b.calculateBarArea()
  	if len(b.data) > width {
  		b.data = b.data[len(b.data)-width:]
  	}
  }
docs: // AddData appends a new bar to a chart