June 19, 2024

Another E-Voting Glitch: Miscalibrated Touchscreens

Voters casting early ballots in New Mexico report that the state’s touchscreen voting machines sometimes record a vote for the wrong candidate, according to a Jim Ludwick story in the Albuquerque Journal. (Link via DocBug)

[Kim Griffith] went to Valle Del Norte Community Center in Albuquerque, planning to vote for John Kerry. “I pushed his name, but a green check mark appeared before President Bush’s name,” she said.

Griffith erased the vote by touching the check mark at Bush’s name. That’s how a voter can alter a touch-screen ballot.

She again tried to vote for Kerry, but the screen again said she had voted for Bush. The third time, the screen agreed that her vote should go to Kerry.

She faced the same problem repeatedly as she filled out the rest of the ballot. On one item, “I had to vote five or six times,” she said.

Michael Cadigan, president of the Albuquerque City Council, had a similar experience when he voted at City Hall.

“I cast my vote for president. I voted for Kerry and a check mark for Bush appeared,” he said.

He reported the problem immediately and was shown how to alter the ballot.

Cadigan said he doesn’t think he made a mistake the first time. “I was extremely careful to accurately touch the button for my choice for president,” but the check mark appeared by the wrong name, he said.

In Sandoval County, three Rio Rancho residents said they had a similar problem, with opposite results. They said a touch-screen machine switched their presidential votes from Bush to Kerry.

County officials blame the voters, saying that they must have inadvertently touched the screen elsewhere.

My guess is that the touchscreens are miscalibrated. Touchscreens use one mechanism to paint images onto the screen, and a separate mechanism to measure where the screen has been touched. Usually the touch sensor has to be calibrated to make sure that the coordinate system used by the touch sensor matches up with the coordinate system used by the screen-painting mechanism. If the sensor isn’t properly calibrated, touches made on one part of the image will be registered elsewhere. For example, touches might be registered an inch or two below the place they really occur.

(Some PDAs, such as Palm systems, calibrate their touchscreens when they boot, by presenting the user with a series of crosshairs and asking the user to touch the center of each one. If you’re a Palm user, you have probably seen this.)

Touchscreens are especially prone to calibration problems when they have gone unused for a long time, as will tend to happen with voting machines.

My guess is that few poll workers know how to recognize this problem, and fewer still know how to fix it if it happens. One solution is to educate poll workers better. Another solution is to avoid using technologies that are prone to geeky errors like touchscreen miscalibration.

This is yet another reminder to proofread your vote before it is cast.

UPDATE (3:15 PM): Joe Hall points to an argument by Doug Jones that problems of this sort represent another type of touchscreen calibration problem. If the voter rests a palm or a thumb on the edge of the touchscreen surface, this can (temporarily) mess up the screen’s calibration. That seems like another plausible explanation of the New Mexico voters’ complaints. Either way, touchscreens may misread the voter’s intention. Again: don’t forget to double-check that the technology (no matter what it is ) seems to be registering your vote correctly.


  1. your 3:15 update isn’t correct; it’s *not* a calibration problem. The calibration is entirely correctly, but the press detection circuitry reports the raw coordinates as being halfway between touch-point A and touch-point B. It’s a design flaw in most touchscreens I’ve used — but it is *not* a problem with the calibration.

  2. A company called Silicone Gaming makes touchscreen slot machines that I’ve used a lot in the past, and every once in a while you run into one that’s miscalibrated — you have to touch somewhere off the spot where the onscreen button is to activate the button. This isn’t an odd or unusual problem; it’s a common enough glitch.

    That anyone connected with touchscreens in voting might think this problem is unusual (or even non-existent) is the scariest part of this problem. It shows that the people involved have the sort of limited experience with computers that also marks so many legislative efforts.

  3. Actually, it’s more than likely not a miscalibration of the touchscreens.

    As Doug Jones points out here[1] people frequently place their hands on the monitor such that one digit (usually the thumb) is pressing the touchscreen inadvertantly in another area. This can shift the the touchscreen grid towards where on the screen the errant digit is placed.

    [1] page 22 of http://www.cs.uiowa.edu/~jones/voting/miamitest.pdf

  4. Bruce Heerssen says

    Indeed, without a paper “receipt” there is absolutely no way to quantify whether the vote presented on screen as any bearing at all on how the vote was registered. As a computer professional, I can attest to the fact that such misdirections are extrordinarily easy to accomplish. My own precinct uses such machines, and without a paper trail. You can bet that I will be asking about alternate voting methods come next Tuesday.

  5. If it really is a miscalibration question, it really is scary. Ms. Griffith (for example) kept pushing buttons until she got the Kerry light to light up, but what did that “Kerry” light correspond to on the back end???

  6. Having worked with touchscreen kiosks and their end-user support in the past, I can vouch that this does sound a little like miscalibration.

    However, I can also vouch that part of the standard setup for these machines probably includes a calibration step, and this is very easy for non-technical people to grasp; so I doubt miscalibrated touchscreens are the actual cause of the problem in this case.

    The suggestion from the unnamed county officials sounds more likely IMO. Those touchscreens essentially average out touch signals from multiple points, so brushing a hand, elbow, or palm against the lower part of the screen would indeed cause the registered signals to appear halfway between the desired point and the accidental-touch point.

    This doesn’t take away from the suggestion that geeky tech like touchscreens should be avoided for e-voting — in fact it makes that suggestion stronger!