index of difficulty is zero while the slope (“b”) represents the inverse of the motor system information-processing rate.This lab will involve examination of how changing the difficulty of the movement (and thus the accuracy requirements) affects the speed of movement (measured by movement time). The width (w) and index of difficulty have an indirect relationship. Fitts’ Law Index of Difficulty Evaluated and Extended for Screen Size Variations, User Interfaces, Rita Matrai, IntechOpen, DOI: 10.5772/9496. That much is obvious, even if the precise relationship is a little surprising. According to Fitts’ law, movement time scales linearly with a single quantity, the index of difficulty (ID), which quantifies task difficulty through the quotient of target width and distance. which means as the width decreases, the index of difficulty increases. If you make targets larger and closer to the user, they'll be easier to get to. Named the Index of difficulty, D is the distance from the starting point to the center of the target. One of the clear takeaways from Fitts' Law is that the Index of Difficulty is inversely proportional to the target Width. Both statements are in accordance with common sense. Thus, the longer the distance and the smaller the target’s size, the longer it takes. Fitts's Law. move the mouse to a certain point in the UI of an application and select it, Fitts's law desribes how the distance from start point to the target and the width of the target influence the index of difficulty (ID) of the task. The Fitts' law methods used in the standard are summarized and software tools are presented that implement the methods. Index of difficulty formulation in Fitts' law was evaluated from the viewpoint of consistency in widget size&distance design variations. Fitts’ law states that the amount of time required for a person to move a pointer (e.g., mouse cursor) to a target area is a function of the distance to the target divided by the size of the target. Fitts’s Law - Modeling Target Movement Time in HCI. Fitts' law is an empirical rule of thumb which predicts the time it takes people, under time pressure, to reach with some pointer a target of width W located at a distance D. It has been traditionally assumed that the predictor of movement time must be some mathematical transform of the quotient of D/W, called the index of difficulty (ID) of the movement task. The term log 2 ( 2A / W ) is called the index of difficulty (ID). 1/b is also called the index of performance (IP) and measures the information capacity of the human motor system. Fitts’ law states that it takes more time to hit a target if the target is further away and it also takes more time if the target is smaller. Fitts’ law is centered around a mathematical equation that is used to illustrate the time it takes to reach a target object. Fitts' law evaluations of computer input techniques are more consistent in recent years due to the emergence of ISO 9241-9, an ISO standard for evaluating input devices. It was found that ID in Eq. Fitts' law also states that the target acquisition time increases drastically if the target gets tiny. Fitts’ law is a factual model used to represent the speed accuracy trade off features of human muscle movement, with analogy method to Shannon’s channel capacity theorem. W is the width of the target. Index of difficulty (ID) is defined by Fitts’ law. For a given target acquisition task, e.g. Effects of Gain and Index of Difficulty on Mouse Movement Time and Fitts’ Law Abstract: The mouse, being the major means of inputting and controlling data on a computer, should beset right for best performance. As … Available from: It describes the difficulty of the motor tasks. 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