Pointing at stationary targets such as buttons, windows, images, menu items, and controls on computer displays is commonplace and has a well-established modeling tool for analysis - [[Fitts's law|Fitts's law]] (Fitts, 1954) - which states that the time to make an aimed movement (MT) is a linear function of the index of difficulty of the movement: '''''MT = a + bID'''''. The index of difficulty (ID) for any given movement is a function of the ratio of distance to the target (D) and width of the target (W): '''''ID =''''' '''log<sub>2</sub>''(2D/W) -''''' a relationship derivable from [[information theory]].<ref name=":1" /> Fitts' law is actually responsible for the ubiquity of the computer [[Mouse (computing)|mouse]], due to the research of Card, English, and Burr (1978). Extensions of Fitt's law also apply to pointing at spatially moving targets, via the ''[[steering law]]'', originally discovered by C.G. Drury in 1971<ref>{{Cite journal|last=DRURY|first=C. G.|date=1971-03-01|title=Movements with Lateral Constraint|journal=Ergonomics|volume=14|issue=2|pages=293–305|doi=10.1080/00140137108931246|issn=0014-0139|pmid=5093722}}</ref><ref>{{Cite journal|last1=Drury|first1=C. G.|last2=Daniels|first2=E. B.|date=1975-07-01|title=Performance Limitations in Laterally Constrained Movements|journal=Ergonomics|volume=18|issue=4|pages=389–395|doi=10.1080/00140137508931472|issn=0014-0139}}</ref><ref>{{Cite journal |doi = 10.1109/TSMC.1987.4309061|title = Self-Paced Path Control as an Optimization Task|journal = IEEE Transactions on Systems, Man, and Cybernetics|volume = 17|issue = 3|pages = 455–464|year = 1987|last1 = Drury|first1 = Colin G.|last2 = Montazer|first2 = M. Ali|last3 = Karwan|first3 = Mark H.|s2cid = 10648877}}</ref> and later on rediscovered in the context of human-computer interaction by Accott & Zhai (1997, 1999).<ref>{{Cite journal|last1=Accot|first1=Johnny|last2=Zhai|first2=Shumin|date=1997-01-01|title=Beyond Fitts' Law: Models for Trajectory-based HCI Tasks|journal=Proceedings of the ACM SIGCHI Conference on Human Factors in Computing Systems|series=CHI '97|___location=New York, NY, USA|publisher=ACM|pages=295–302|doi=10.1145/258549.258760|isbn=0897918029|s2cid=53224495}}</ref><ref>{{Cite journal|last1=Accot|first1=Johnny|last2=Zhai|first2=Shumin|date=1999-01-01|title=Performance Evaluation of Input Devices in Trajectory-based Tasks: An Application of the Steering Law|journal=Proceedings of the SIGCHI Conference on Human Factors in Computing Systems|series=CHI '99|___location=New York, NY, USA|publisher=ACM|pages=466–472|doi=10.1145/302979.303133|isbn=0201485591|s2cid=207247723}}</ref>
==== [[Control theory|Manual Control Theory]] ====
