@article{ref1,
title="Spacing requirements for visual display of Markov constraints",
journal="Human factors",
year="1973",
author="Pollack, I.",
volume="15",
number="4",
pages="395-400",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0018-7208",
doi="",
url="http://dx.doi.org/"
}