How to change GRID (two possible ways):
plot.setRangeStep(XYStepMode.INCREMENT_BY_VAL, 125); plot.setDomainStep(XYStepMode.SUBDIVIDE, 16);
How to change the thickness of the line of the chart: You need to change the LineAndPointFormatter that you use in this way (initializing Paint with the current lineAndPointFormatter paint is important, otherwise you will get really strange behavior):
LineAndPointFormatter lineAndPointFormatter = new LineAndPointFormatter( Color.rgb(0, 0, 0), null, null);
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