Beginning with Strategy Mobile 9.4.1 iOS Update 2, users can zoom in/out of individual graphs present in dashboards. This can be done using pinch open/close gesture on the device to stretch the X and Y axes.

As shown in the above image, pinching in the directions denoted by the arrows causes zooming of the graph in those directions.
This applies to single or multiple series graphs. The zooming-in scale for the single chart case is three times the intial scale.