This option is available on full-screen chart cards in both portrait and landscape mode.
When a chart displays many values, some axis labels may be hidden to aid readability. However, when you zoom in, previously-hidden axis labels become visible.
To zoom in on a chart, place your index finger and thumb on the screen, and move them apart. This enlarges the selected area.
To zoom out, place your index finger and thumb on the screen, and pinch them together. This restores the view to its original size.