Known issue: scrolling a zoomed-in chart interferes with swiping to the
next/previous chart (so far there's just one, but...)
Workaround: Swipe down and then left or right in one go, this will let
you scroll the zoomed chart
- use just one data set, because multiple data sets is not supported
by MPAndroidChart (the way we need it)
Now there is hardly any space between the bars anymore
Also:
- allow scaling x and y axis independently via pinch gesture
- set fixed y max value (1.0) so that the display is stable and
independent of the actual available data
- (at least temporarily) display y labels