Render drawings in 3 different density modes:

non-Retina mode
Retina mode
Infinite mode

Non-Retina mode shows you how your drawings will look like on non-Retina displays (most Macs) Retina mode draws with double density - this is how your drawings will look on Retina displays (most iOS devices). Finally, the Infinite precision mode previews your drawings with infinite precision - no matter how far you'll zoom in, the drawings won't be pixellated.