Fitts’s Law Incredibly professional presentation by Thomas Gin, someone please hire me

Introduction Created by American psychologist Paul Fitts Law that predicts the average time for someone to move and interact with some target Mathematical equation

Fitts’s Law MT = a + b (ID)

ID = log2(2D/W) Index of Difficulty ID = way of measuring difficulty of selecting a target D = distance from starting point to center of target W = width of the target from axis of motion

ID = log2(2D/W) Index of Difficulty Difficulty of interaction increases when the target is farther away Difficulty of interaction decreases when the target is larger

Why 2D Instead of D?? “The use of 2A rather than A is indicated by both logical and practical considerations. Its use insures that the index will be greater than zero for all practical situations and has the effect of adding one bit (-log21/2) per response to the difficulty index. The use of 2A makes the index correspond rationally to the number of successive fractionations required to specify the tolerance range out of a total range extending from the point of initiation of a movement to a point equidistant on the opposite side of the target.” - notable smart man, Paul Fitts

MT = a + b (ID) = a + b log2(2D/W) Fitts’s Law MT = a + b (ID) = a + b log2(2D/W) MT = average time to complete movement a = constant for starting/stopping time of the device b = constant for inherent speed of the device

IP = (ID/MT) or IP = 1/b Index of Performance IP = way of measuring human performance Fitts’ version is the first one MT = a + ID/IP

Takeaways from Fitts’s Law Important targets should be larger Buttons > hyperlinks Make radio button text clickable Users have small areas of attention Keep tasks and task relevant targets close together Targets in corners and screen edges are easier to hit due to limitations on movement

Takeaways from Fitts’s Law Consider how users will read your webpage when placing elements Linear menus can take longer to navigate Radial menus give equal importance to all clickable elements Doesn’t only apply to mouse based movement or even computers

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