All knobs recognize rotational gestures. For normal touch response, use the outer edge of the knob image.
Drag away from a knob's center for increased control over fine adjustments.
When working with dual-concentric knobs, the center knob will be active by default. Press and hold for one second to switch focus to the outer knob.
Press the zoom button to toggle between min/max zoom settings.
Use two fingers to pinch-zoom between min/max zoom settings.
Use two fingers to scroll/pan when zoomed in on a device.