of N straight tunnels, numbered 1 through N, each located at si where i = 1 to N, and each of length si+1 − si and of width W(si). We can let N grow arbitrarily large, making the length of successive straight tunnels become infinitesimal. The total time to navigative through the curved tunnel is yielding the general form of the steering law. Modeling steering in layers Steering law has been extended to predict movement time for steering in layers of thickness t (Kattinakere et al., 2007). The relation is given by See also Crossing-based interface — any graphical user interface that uses goal crossing tasks as the basic interaction paradigm References Johnny Accot and Shumin Zhai (1997). Beyond Fitts' law: models for trajectory-based HCI tasks. Proceedings of ACM CHI 1997 Conference on Human Factors in Computing Systems, pp. 295–302. http://doi.acm.org/10.1145/258549.258760 http://www.almaden.ibm.com/u/zhai/papers/steering/chi97.pdf Johnny Accot and Shumin Zhai (1999). Performance evaluation of input devices in trajectory-based tasks: An application of the steering law. In Proceedings of ACM CHI 1999 Conference on Human Factors in Computing Systems, pages 466–472. http://www.almaden.ibm.com/u/zhai/papers/steering/chi97.pdf Johnny Accot and Shumin Zhai (2001). Scale effects in steering law tasks. In Proceedings of ACM CHI 2001 Conference on Human Factors in Computing Systems, pages 1–8. http://doi.acm.org/10.1145/365024.365027 http://www.almaden.ibm.com/u/zhai/papers/EASEChinese/Scale.pdf Kattinakere, Raghavendra S., Grossman, Tovi and Subramanian, Sriram (2007): Modeling steering within above-the-surface interaction layers. In Proceedings of ACM CHI 2007 Conference on Human Factors in Computing Systems 2007. pp. 317–326. http://doi.acm.org/10.1145/1240624.1240678 http://www.dgp.toronto.edu/~tovi/papers/chi%202007%20steering.pdf Shumin Zhai and Johnny Accot and Rogier Woltjer (2004). Human Action Laws in Electronic Virtual Worlds: An Empirical Study of Path Steering Performance in VR. Presence, Vol. 13, No. 2, April 2004, 113–127. http://www.almaden.ibm.com/u/zhai/papers/LawsOfActionManuscript.pdf Contains references to, and discusses differences with, earlier work on the "steering law" by Rashevsky and by Drury. External links http://www.almaden.ibm.com/u/zhai/topics/LawsOfAction.htm Human–computer interaction