When we asked people to share their stories of voting irregularity earlier today, dozens of people shared this video — currently on the Reddit front page with nearly 20,000 up-votes — of a Pennsylvania voting machine seemingly altering a man's vote from Obama to Romney. We reached out to Joseph Lorenzo Hall, Senior Staff Technologist at the Center for Democracy & Technology, to ask his opinion; here's what he told us:

It's a concern but not because of fraud... that's an obviously miscalibrated iVotronic (ES&S) voting machine... we would recommend that poll workers would recalibrate the machine and everything would be fine. Also, with some models of voting system if you place a thumb on accident while resting on the machine it can "bias" the calibration of the touchscreen up towards the errant thumb. That could be happening to, if it's only for this one voter.

Hall, currently manning the D.C. election protection command center and answering questions on Twitter, just gave an excellent interview to The Awl's Maria Bustillos. Here's his "number-one recommendation" for voters worried about irregularities:

The number-one recommendation I can make is make sure voters "check their work"; that is, if you're voting on a voting machine, it will usually summarize your selections on a final screen before you cast your vote (and if there is a paper trail-a printer on the side, be sure to carefully make sure it prints your choices correctly). Make sure this ballot summary reflects how you want to vote because this is the most likely step where voters would make a mistake or an attacker would try and take advantage of an inattentive voter and show something different on the screen versus the paper. If you have a problem, tell the poll workers and then call us at (non-partisan) Election Protection at 866-OUR-VOTE.