I would like a long operating distance (about 150~250cm) eye-tracker, so maybe the VT2-XL is my choice. But the system requirement of VT2-XL is "Up to 50 in (127 cm) Monitor" and my monitor is about 17 inches (4:3).

Does a VT2-XL work on small monitors? Or is it accurate on small monitors?


asked 09 Mar '15, 05:06

KYO's gravatar image

accept rate: 0%

edited 09 Mar '15, 14:54

phyatt's gravatar image

phyatt ♦♦

I am interesting about the gaze data(x,y coordinate) or gaze point on my screen.

So in my case, there is a 1.3cm error or 1.3 cm range floating on my gaze point right?

I very appreciate for helping me.

(10 Mar '15, 01:06) KYO

1.3 cm standard deviation. The error or the precision varies from person to person, but a typical error value is also near to 0.5 eye degrees. Some people have almost no error. Wearing glasses, or hard contacts can cause more error.

(10 Mar '15, 02:44) phyatt ♦♦

Short Answer

Yes, the VT2 XL does work on a small monitor, though you may have trouble hitting/clicking on small buttons. Larger buttons are recommended for long distances.

Long Answer

The accuracy of an eye tracker is measured in eye degrees. So the end accuracy on a small monitor may appear more course.

When calibrated you can expect accuracy to about 1/2 an eye degree on the screen you are using.

eye tracking diagram, showing eye degrees

17" monitor with 4:3 aspect ratio has dimensions of 35 cm x 26 cm.

The accuracy of an eye tracker has some limitations from the jitter of eye movements and eye muscles (saccades).

tan(theta) = opposite/adjacent
tan(eye degree accuracy) = accuracy height  / distance to monitor
tan(0.5 degrees) = (accuracy height) / 150 cm
accuracy height = 150 cm * 0.00872
accuracy height = 1.3 cm

accuracy % = (1.3 cm / 26 cm) * 100
accuracy % = 5%

So for an individual user that has done a full 16 point calibration across the screen, they could possibly hit small buttons, 1.3 cm in height, from 150 cm away. The realistic, easy-to-use button size is about 6 to 10 times the eye degrees accuracy size, and sometimes higher for public display kiosks with rough calibrations.

In our QuickACCESS software we make the buttons range in size from: 3.5 cm to 4.5 cm for typical use cases at 60 cm away. These button sizes in eye degrees are: 3.3° to 4.3°.

Kind of like on touch screens, you can use small buttons if you NEED to, but most of the time you prefer buttons that are larger and easier to hit. Eye tracking is very similar.


answered 09 Mar '15, 14:46

phyatt's gravatar image

phyatt ♦♦
accept rate: 8%

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Asked: 09 Mar '15, 05:06

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Last updated: 10 Mar '15, 02:44

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