Posters are big and cumbersome, and hanging them up yourself is tricky. You have to unroll it, stick a tack in one of the upper corners. Then you have go try to stick a tack in the other top corner, maybe two meters away, which is often longer than armspan for something above shoulder height.
Now step back and check that the top and bottom edges are horizontal.
Do not trust your instincts about the level line from when you stuck in that second tack. The upper corners of your posters are almost always above your eyeline, making it difficult to judge whether the poster is level or not.
If you think this goes without saying, I beg to differ. At Neuroscience recently, I was astonished at how many posters looked like they were taking on water on one side. These were not subtle little “one corner is higher” problems. I saw several that I guess were about five degrees off true.
The easiest way is to have a friend or colleague or helpful conference goer who is willing to step back and do the old, “Up a little bit... down a little... a little more... perfect!”
If there’s nobody else around, you can mount one edge of your poster flush with the posterboard. This has the downside that if can look a bit odd if your poster is much smaller than the posterboard, though.
Finally, since we are living in the future, there is, as they say, an app for that.
Photo by L. Marie on Flickr; used under a Creative Commons license.