I've noticed that sometimes when I add annotations they look a little bit blurry. After some investigation I have discovered that the chart frame has subpixel alignment issues:
print (CGRect)[self.chart getGLFrame]
(CGRect) $1 = origin=(x=70.5, y=0) size=(width=953.5, height=735.5)
I know getGLFrame is deprecated but this is the frame that the annotation is being added into. Turning on "color misaligned images" in the simulator confirms that the annotation is misaligned.
I've also noticed that the labels on the axis are often blurry and show up as misaligned as well. I think this could be caused by the same issue.