Here are some handy tips for getting right into the detail of proofs:
0, 1, 2, 4 will zoom the proof (fit, 100%, 200%, 400%) – up and down arrow keys to move through the zoom positions, shift + up and shift + down will nudge the zoom by 5%.
z + scroll will zoom between these zoom states.
Tips for zoom
For those on mobile devices and tablets, pinch to zoom.
To zoom in to a particular area of the proof, place the mouse pointer on the area and use the scroll wheel to zoom in/out.
For more handy keyboard shortcuts take a look at this article.