"Have you ever used a signature pad" on an electronic check-out system in a retail store, he asked. "It looks nothing like your real signature 99% of the time. It looks like crap. That's why we don't use touch-screens."

And though it didn't show up in the design stages of the eSlate, a usability issue did once turn up in California, he said. "In one county, sometimes people were relaxing and leaning on the 'cast ballot' button and casting their ballot unintentionally."

To fix that, election officials increased voter education efforts, reminding them not to lean on the machines while casting their votes, he said.

A spokesman for Sequoia Voting Systems of Oakland, Calif., could not be reached for comment.

David Beirne, the executive director of the Election Technology Council, a Houston-based trade group that represents e-voting vendors, said that "most if not all of them did some sort of usability testing before production."