When I include comments, highlights, or other notes on students' written submissions, often they are unable to see where my notes are supposed to be; that is, the highlights are floating in space and my comment arrows are pointing in a different place than where I put them. Any ideas on why this happens? Sometimes, when I return to a graded document, those marks are in different places too even though I always use the same machine for my grading (MacAir, Safari browser). It's more frustrating than anything, because I (and students) have to spend time to make sense of my arrows and notes belong before dealing with their real content. Thanks!