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[[FILE:SamuelBakQuiteClear.jpg|border|right|thumb|link=http://chgs.elevator.umn.edu/asset/viewAsset/57f3b6787d58ae5f74bf8ba9#57f3b6d77d58ae5574bf8bcb| [[Arts#:Category:Samuel Bak|Samual Samuel Bak]], Quite Clear <ref>[http://chgs.elevator.umn.edu/asset/viewAsset/57f3b6787d58ae5f74bf8ba9#57f3b6d77d58ae5574bf8bcb Chess in the Art of Samuel Bak], [http://chgs.elevator.umn.edu/ Center for Holocaust & Genocide Studies], [https://en.wikipedia.org/wiki/University_of_Minnesota [University of Minnesota]]</ref> <ref>The mountain in the background looks like [https://en.wikipedia.org/wiki/Torghatten Torghatten] near [https://en.wikipedia.org/wiki/Br%C3%B8nn%C3%B8ysund Brønnøysund]</ref> ]]

a measure of the number of choices ([[Legal Move|legal moves]]) a player has in a given position. It is often used as a term in the [[Evaluation Function|evaluation function ]] of chess programs. It is based on the idea that the more choices you have at your disposal, the stronger your position. A study by [[Eliot Slater]] of 350 tournament games in which the material balance was still even after the 20th move showed a definite correlation between a player's mobility and the number of games won <ref>[[Eliot Slater]] ('''1950'''). ''[http://www.eliotslater.org/index.php/chess/147-statistics-for-the-chess-computer-and-the-factor-of-mobility Statistics for the Chess Computer and the Factor of Mobility]''. Proceedings of the Symposium on Information Theory, London. Reprinted ('''1988''') in [[Computer Chess Compendium]], pp. 113-117. Including the [http://www.eliotslater.org/index.php/chess/159-discussion-on-the-above-paper-alan-turing-et-al-1950 transcript of a discussion] with [[Alan Turing]] and [[Jack Good]]</ref> .

[[Freedom]] and [[Papa]] both use [[Mobility|mobility]] as their primary term in their [[Evaluation functionFunction|evaluation functions]]. As with [[Awit|Wita]], both use the ratio of computer's moves / opponent moves. Papa and Wita also multiply by the ratio of the [[Square Control|squares controlled]] and Papa goes one step further and takes the [https://en.wikipedia.org/wiki/Logarithm logarithm] of this product to form the "[[Papa#Entropy|entropy]]" of the position. The true merit of this entropy over the product ratio was not made clear, but it does ensure that in extreme situations the evaluation remains more closely bounded.

[[Dan Heisman]] <ref>[[Dan Heisman]] ('''1990, 1999, 2010, 2015''').''[http://www.danheisman.com/elements-of-positional-evaluation.html The Positional Elements of ChessPositional Evaluation]''. Russell Enterprises</ref> represents an attempt at mathematical abstraction applied to chess, introducing seven concepts as fundamental in analyzing a chess position: mobility, flexibility, vulnerability, [[Center Control|center control]], piece coordination, time and speed. Heisman applies two [https://en.wikipedia.org/wiki/Dichotomy dichotomies]: ''actual'' versus ''potential'' and ''local'' versus ''global'':

| style="text-align:center;" | All reachable squares</br/>from this position

Quote by [[Alan Turing]] on [[Eliot Slater|Slater's]] 1950 paper ''Statistics for the Chess Computer and the Factor of Mobility''. <ref>[[Eliot Slater]] ('''1950'''). ''[http://www.eliotslater.org/index.php/chess/147-statistics-for-the-chess-computer-and-the-factor-of-mobility Statistics for the Chess Computer and the Factor of Mobility]''. Proceedings of the Symposium on Information Theory, London. Reprinted ('''1988''') in [[Computer Chess Compendium]], pp. 113-117. Including the [http://www.eliotslater.org/index.php/chess/159-discussion-on-the-above-paper-alan-turing-et-al-1950 transcript of a discussion] with [[Alan Turing]] and [[Jack Good]]</ref> <ref>[http://www.turing.org.uk/sources/info50index.html Conference on Information theory, 26-29 September 1950]</ref>:

* [https://groups.google.com/d/msg/rec.games.chess/6vwtkcF6sRU/4M3oOiDNYwgJ Mobility Measure: Proposed Algorithm] by [[Dietrich Kappe]], [[Computer Chess Forums|rgc]], September 23, 1993