Next Tuesday’s presidential election will likely be extremely close, magnifying the potential impact of vote-counting errors. So it could be problematic that several states rely on computerized voting machines that don’t print out a paper record that can be verified by voters and recounted by election officials if necessary.

 

Such machines are in use in 17 states, as indicated in red on the map above. Computer scientists and fair-election advocates have warned for years that potential software malfunctions are possible threats to the integrity of elections in counties and states that use these machines.

Another 13 states, including battleground states such as Nevada, Wisconsin, Ohio, and North Carolina, have at least some polling stations that use voting machines with a precautionary measure: a receipt that can be checked later—a so-called voter-verified paper audit trail. These machines are still vulnerable to software glitches, but voters at least have a chance to spot errors and make sure their vote gets registered and recorded accurately.