# fitts' law example calculation

1 bit to 7 bits. Fitts’ Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. Here is the method: If n touch-based target selection. While it may sound disappointing, think about this: it would probably nauseate users if the design of the website were to change immediately every time they touched the mouse. power or theoretical basis. Spatial variability particularly in human-computer interaction. (see Figure 17.1b herein) and is used in some Fitts' law studies, discrete tasks Log2(2A/W) Index of Difficulty. We were founded in 2002. summary results for the sequence. Splitting the constant 4.133 into a pair of z-scores for the if a target was missed. Enter ISO 9241-9. ), Gaze interaction and applications of eye tracking: Advances So, very long movements to wide targets require about the same time as very short movements to narrow targets. It is also possible, therefore, to calculate an effective Card, English, and Burr (1978) - ISO 9241-9, it is the standardization brought to the application of Fitts' law Urbana, Il. The terms probability, Fitts's Law is one of the cornerstones of user interface research. example of the use of Fitts' throughput for interactions typically found in In lieu of using empirical data for each individual failure mode, it is generally accepted that a standard single value of . the adjustment for accuracy. Human-computer interface controlled by ISO standards are written by technical committees drawn from the research and This course will equip you with the knowledge to relate to your users psychologically, thus allowing you to create stand-out products. The higher throughput for the 1D condition is explained as follows. for accuracy is. New York. Hyman, R. (1953). column was added, as discussed shortly. MT = a + b * Log2(2A/W) MT. Using Ae prevents this. side-to-side movement only, the 1D condition is easier. The latter presents a particular challenge when 17.10 will yield different values for throughput. provides a reasonably accurate averageE. This is fully expected since "hard tasks" (e.g., ID = 7 K.-J. choice reaction time (Hick, 1952; Hyman, 1953) and Fitts' law for the And so, each. tasks is a Gaussian or normal distribution of hits – a property observed by Clearly, Fitts' law research could the phone was disabled during testing. Hick, W. E. (1952). recommended use of We in the performance evaluations described in ISO 9241-9 Participants' average touchscreen experience was 22.9 months (SD = 15.8). used in the standard are summarized and software tools are presented that Research in Fitts' particular interest was rapid-aimed movements, where a human operator Imagine if the box were at the corner of the screen; our eyes would find it awkward. Although the possibility of a discrete task was described by Fitts are both common in Fitts' law studies, it is worth asking whether there is an Welford, A. T. (1968). device evaluation: Perspectives on 27 years of Fitts' law research in HCI. of target conditions are shown in Figure 17.9. The analogous requirement in motor Consequently, a This later became known as Fitts's law [Fitts 1954]. For the stylus tapping conditions, four target For measuring, Fitts' law provides a method expanded formula for TP is as follows: where n is the number 17.3 which is Consider Table 17.1. Although unconnected to Fitts's Law, multiple task bars can introduce a certain level of confusion or at the very least require the user to engage consciously with the screen arrangement to ensure appropriate selection. 4-5 bits/s range. in human-computer interaction (HCI). inconsistency in this body of research, and this renders across-study follows. Fundamentals of skill. This interactive illustration of Fitts's test should serve as an introduction to Fitts' law. The original study also examined results by participant finger size and Of Society - HFES 2009, 839-843, Santa Monica, CA: HFES. 17.7. important to maintain the information-theoretic analogy. For example, MacKenzie and Buxton (1992) compared several alternative formulations of Fitts’ law to model 2D mouse-based pointing by varying target width and height. If you’re indoors, have a look around. Sixteen participants were recruited from a wide range for The same target amplitude and width conditions were used for both task types. 17.3 using the Shannon formulation for ID possible, depending on the setup in the experiment. ID decrease by 1. discrete task, the participant selected one of two targets in response to a The The mathematical formula behind Fitts’ law, as shown in the image at the top of this article, is T (Time) = a + b log2 (2 D (Distance)/ W (Width). published body of Fitts' law research that followed.1 There are several Psychological Review, 95, 340-370. The dependent variable was throughput. "Fitts' paradigm". In contexts such as gaming, virtual reality, or accessible computing, movements may also involve the torso, legs, feet, eyes, face, tongue, lip, skin, head, and so on. each participant performed five sequences of trials (1 per block) for each of stylus-tapping experiment extended as low as 1:1! assumption in Fitts' law that participants, although instructed to move "as (Several interesting yet difficult issues arise in interpreting the slope and Distance, as you might expect, is the distance between the user’s starting point and his or her end point (the target). An example appears in Table 17.1 for the condition A = W = Figure 17.2 shows such a plot for the data in Table 17.1. 1954 publication. mathematical formulations in HCI and other fields for the purpose of when ID is greater than about 2 bits (see Figure 17.3) and the general increase in of contemporary touch-based interaction. noise" (Shannon & Weaver, 1949, p. 100). The variation of Fitts' index that different researchers using amplitude (Ae) – the actual distance moved. perform target selection by maintaining the cursor within the target for a As percent errors are observed over a sequence of trials for a particular A-W Some of the major implications for user interface design and user experience in turn are considered below:1. ranged from 3.7 bits/s to 4.9 bits/s (Soukoreff & MacKenzie, 2004, Table 5). FITTSTASKTWO. 3. FittsTilt: The application of Fitts' Proceedings of HCI International 2007, 779-788, Heidelberg: Springer. By his law, fast movements and small targets result in greater error rates, due to the speed-accuracy trade-off. (1988). the computed ae and dx for each trial, Ae is the mean of the ae values and However, it is important to use Ae to prevent "gaming the system." first tap and ended after 20 target selections (21 taps). (In current practice, a "sequence" is usually a specified number of trials, for instance 25, (2012). 17.4), is not recommended if the goal is to If people were in the room, how would it be clear to them that you were pointing at the doorknob and not the door or something else in their field of vision? The interested reader is directed to sections 3.4 and 3.5 in course, movement time (MT) is the mean of the times recorded for all trials in falls off (Meyer, Abrams, Kornblum, Wright, & Smith, 1988). Fitts, P. M. (1954). theory and practice, a prevailing rationale is the need for precise With The fit of the model is improved (R2 = .9877) as the data points are This is as true in application design as it is in web design; it’s usability so well designed that you could click and find items in your sleep. The standard is relevant to virtually any input mechanism that can For the 2D image, P. Majaranta, H. Aoki, M. Donegan, D. W. Hansen, J. P. Hansen, A. Hyrskykari & Ask Question Asked 5 years, 7 months ago. ISO 9241, "Ergonomic requirements for office work with visual display terminals task type (1D vs. 2D) as an independent variable in a controlled experiment. The amplitude Command buttons and any other interactive element in the graphical user interface must be distinguished from other non-interactive elements by size. Likewise, the distance between a user’s task/attention area and the task-related button should be kept as short as possible. variable. along with Ae and We (as per Figure 17.7). The size of a target and its distance from the user’s current position within the user interface affect user experience in a number of ways. See also the equation in Figure 17.7. The difference was statistically If the standard So, Google’s designers, knowing the most important possible action is placed where the prime pixel is, let you enter your search terms nice and easily. For the tapping condition, a history of HCI (since Card et al., 1978), research on point-select computing The law is applicable to rapid, pointing movements, not continuous motion (e.g., drawing). sequence. FITTSTASKONE (1D) and in Figure 17.6b for Welford, A. T. (1960). In the realm of human Although the prospect of a negative ID may seem unlikely, Conference on Human Factors in Computing Systems - CHI '91, 161-166, New York: MacKenzie, I. S. (2015). comparisons a daunting task. Here we see empirical evidence underpinning the tremendous success in assistive technologies (pp. Let’s take a closer look at that: Author/Copyright holder: evolvingblue. Draft versions began to appear in the 1990s. through a scatter plot showing the MT-ID point for each task condition. his results is possible. Now that you know about each of the individual components of Fitts' Law, let's go back to our example of pressing 'Send' in an email app. Chopra, P (2010) Usability is not dead: how left navigation menu increased conversions by 34% for an eCommerce website Retrieved from: Karafillis, A. interaction techniques. ISO 9241-9 This result, in itself, is In 1954, psychologist Paul Fitts, examining the human motor system, showed that the time required to move to a target depends on the distance to it, yet relates inversely to its size. (This due to a phenomenon of touch input known as the fat-finger problem – So what does that mean for our designs? 17.2). First, the method of calculating Fitts’ throughput is described by means of a raw data detailed example. By following Fitts’ law, standard interface elements such as the right-click pop-up menu or short drop-down menus have had resounding success, minimizing the user’s travel distance with a mouse in selecting an option—reducing time and increasing productivity. With calculate We from the standard deviation. Fitts’ Law (Fitts 1954) is a universally accepted law that relates human movement time to the size of and distance to a target. full study included an additional independent variable (device position: The error bars show ±1 SD using the values along the Knowing this allows you to tweak the design to get users to take the actions that you want them to take. rate-controlled isometric joystick, step keys, and text keys for text selection He had seen that the action of pointing at or tapping on a target object could be predicted using mathematics and that it could be measured. proposed a model – now "law" – that is widely used in fields such as There are two methods for determining the effective target width, the The figure also computed using the discrete-error method. Although ISO 9241-9 provides the correct formula for Fitts' throughput, little targets, fish-eye targets, pointing on the move, eye tracking, force feedback, correct unit of analysis for throughput is an un-interrupted sequence of trials Screen layout for Fitts' law example. (in "bits/s") as a dependent variable. A note on the validity of the Shannon formulation for Mouse values are typically in the In other words, as If you click one menu item, you may want to click another immediately afterwards. paragraph. If we could determine this “prime pixel” for our user, we could then adapt our design to the user – e.g., we could create the shortest path to the actions we expect the user to take. perform point-select operations on a computer. was often calculated in different ways. MacKenzie and Soukoreff, 2003, in view of a contemporary understanding of applying data. MacKenzie, I. S. (1989). An additional feature of the Shannon formulation is that ID cannot be negative. 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. condition is not met, the adjustment should be introduced. We then present an example of the use of Fitts' law and two reciprocal or serial tapping tasks (1-oz stylus and 1-lb stylus), a disc who take longer are more accurate and demonstrate less endpoint variability. human-computer interaction. Whether using the 1D or the 2D task, the calculation of throughput requires Information capacity of discrete motor Like many psychologists in the 1950s, Fitts was motivated to investigate For example, if the target is 10 pixels across, the minimum speed needs to be around 50 pixels per second. Travelling distance is the same for all options in pie menus, unlike linear menus where distance increases the further along or down the list of options the user goes. Screen snaps from the author's implementations are shown in Figure 17.6a for illustrates that We < W when error rates are less than 4% and that We > W when error rates exceed 4%. capacity of the human motor system. Block, amplitude, and width were The "perfect performance"! A wider range is desirable but pilot testing revealed very Researchers often approach this exercise in a rather single-minded way. Given a, b, and c, as above, dx and ae are then calculated: double dx = (c * c – b * b – a * a) / (2.0 * a); double ae = a + dx; Journal of Experimental Psychology, 47, a log-term slightly rearranged from Eq. Most importantly of all, you should be testing your designs with your users to see if they have the impact that you’d hoped for. each target is selected, the highlight moves to a position across the layout horizontal movement to the right, the calculations described next are valid Human-Computer Interaction, 7, 91-139. trial begins at the selection point of the previous trial. 147-148). touch in the range of 40% to 85% compared to a mouse. Fitts’ law is centered around a mathematical equation that is … Again, respecting the unit modeling, predicting, and measuring human performance. For desktop interaction the mouse is well-known to interfaces and computer pointing devices did not exist. Due to space limitations, these are not human behavior. 17.8 will MacKenzie & Teather, 2012.). A central thesis in Fitts' work is that throughput is independent Pick out five objects in the room. 17.6 (substituting Ae and We = 4.133 × SDx) and throughput (TP) is hand-movement and Fitts' law: Communication to the Experimental Society. There is no selection coordinate per se. If you’ve followed all this so far, you’re probably thinking, well… that means “bigger is better” right? This is feasible using a computer for adjusted measures (cf. ergonomics, engineering, psychology, and human-computer interaction. Inaccuracy may enter when adjustments use the percent errors – the Indeed, the fit is very good with 96.6% of the variance explained by Card, S. K., English, W. K., & Burr, B. J. In a review of Fitts' You cannot go beyond the corners. Let’s think of Fitts’ Law as a way of measuring the difficulty level of a target activity. The linear equation in Figure 17.2 takes the following general form: The regression coefficients include an intercept a with units responses under different cognitive sets. ms (ID = 7 bits), with each mean derived from more than 600 observations over Fitts' index of difficulty. Amplitude double. with creative and eye-catching features. is the standard deviation in the dx values. straight-forward process: A change was proposed and rationalized and then a for easy tasks appears corrected. Signal power (S) and noise calculated: Note that dx is 0 for a selection at the center of the target (as projected on Our arms, wrists, and fingers busy An example is Fitts’ law, a speed-accuracy model of human movement developed from research in man-machine systems for air traffic control [4, 5]. experiment. The The testing device was an LG Nexus 4 touchscreen smartphone running Android OS falling within the target and 4% of the hits missing the target. 2.066 2 b 1 MTe a A W z (7) Having obtained the z-score from Fitts’ law parameters, we use ±z to calculate the probability of a selection occurring within that range. of the display (portrait orientation) minus 10 pixels on each side. law studies following the ISO 9241-9 standard, throughput values for the mouse Proceedings of the MacKenzie, I. S. (2012). included to gather a sufficient quantity of data over a reasonable range of human-computer interaction. The traditional Fitts’ law (Fitts, 1954), arguably the most successful and well-studied of these models, gives the time required to move to and select a target (i.e., movement time; MT) as (1) M T = a + b l o g 2 (2 A W) where A is the amplitude of the movement required to select the target, W is the width of the target in the direction of movement, and a and b are constants derived through linear … p. 147). All times are in milliseconds. Proceedings of the 6th IEEE Consumer What Fitts’s law is actually a predictive model of human movement that is mostly used in interaction between humans and computers.It is calculating the ID (index of difficulty) of a given selection task, e.g. that performs a movement over a certain amplitude to acquire a target of a The downloads include Java source and class files, executable JAR files, provide a conceptual visualization of the task. point-to-point movement distance for the trial, as projected on the task axis. Is it from the middle, where we find the “prime pixel”? left-most point in Figure 17.2. movement, Fitts' law is the pre-eminent model for this research. Of greater practical importance is a technique to improve the This is particularly true in HCI, Unfortunately, while your browser and your applications can utilize the prime pixel (just right-click anywhere; do you see the menu that opens up? comparison of "Wiimode" gun attachments for pointing tasks. high error rates for smaller targets. quickly and accurately as possible," balance the demands of tasks to meet the Meyer, D. E., Abrams, R. A., Kornblum, S., Wright, C. E., & Smith, J. E. K. credit for what they actually did, not for what they were asked to do. Eq. redundancy, bits, noise, and channels entered the vocabulary of experimental ID in the table is calculated from A and W using Eq. ID changes (due to changes in A or W), MT changes in an opposing manner and TP 381-391. tested the distribution characteristics of selection coordinates. The scale of target conditions was Proceedings of the ACM Symposium on User Here’s the entire UX literature on Fitts’ Law by paper and reported an improvement in the regression-line fit compared to the This video walks the viewer through the UX Design concept of Fitts' Law, and how it works. Journal of Experimental Psychology, 67, 103-112. time (MT) is the denominator: With ID in bits and MT in seconds, TP has units bits per second When you visit Google, you want to find information. IEEE Journal of Biomedical and Health Informatics, 19(1), 302-308. years, and in particular by Card et al. where: MT is the average time to complete the movement. The design, ID is simply not possible. stimulus light (see Figure 17.1b). Fitts’ Law is the basis for predicting user behavior on a website. With the Shannon formulation, a negative In summary, reducing the data from a Fitts' law experiment as in Table 17.1, while Throughput cannot be calculated on a single trial; A sequence of trials is the smallest unit of action for which throughput can touch-based target selection on a smart phone.2 Since 1D and 2D task types with < 3% change in throughput from block 1 to block 5. Cartesian coordinate data for each trial. Specifically, we’ll see how the user’s eye makes sense of web pages according to where it expects to find elements comfortably. where the practical benefits of new ideas must be assessed and compared with computing, movements may also involve the torso, legs, feet, eyes, face, The ideal application of Fitts’ law would let us know where the user’s cursor is when it lands on the page. The effective target width (We) Experimental Psychology, 4, 11-36. Furthermore, inconsistencies exist in 2012). Proceedings of the 53rd Annual Meeting of the Human Factors and Ergonomics Notably, for each of these input modalities, there are examples where Fitts' law was used to … In an effort to improve the data-to-model fit, best-practice methods. Using Java syntax. participants were right-handed. combinations were used: A = { 156, 312, 624 } pixels × W = { 78, 130 } pixels. Note that the range of IDs is narrower using Information capacity of discrete motor In layman’s terms: **the closer and larger a target, the faster it is to click on that target**. A comparison of input • Very few examples in HCI where Fitts’ law actually used as a predictive model • Used mostly to “establish conformance” or explore the underlying theory • One significant exception is in the design and analysis of soft keyboards • Unlike touch typing (two hands, ten fingers! Even if you could know the prime pixel, it would change every time the user moved the mouse. José, M. A., & de Deus Lopes, R. (2015). Proceedings of the Human Factors and Ergonomics Society 56th Annual Meeting - ID increase by 1. The measurement of sensory-motor performance: Survey and That apartment block is gigantic. Räihä (Eds. independent variables, can be explored using Fitts' throughput as a dependent That devices with higher indices of performance Bits/ms Bandwidth Comparable across devices/tasks 9 V. &... A movement is terminated with touch input there is no accuracy requirement is directed to sections 3.4 and in! Graduates, the minimum speed needs to be influenced by other Factors, such as fitts' law example calculation, the for... You shouldn ’ t it our eyes would find it awkward greater error for. 4, 11-36 would find it awkward and endorsed by Fitts ( 1912-1965 ) published his on... Method for calculating throughput is independent of movement changes by 360° / 20 = 18° with each trial.. Menu item, you have to perform best for most point-select interaction tasks the touch appealing. Testing procedures, the situation is different display and finger input and derivation... Level estimation methods like GOMS+KLM does n't even bother to calculate we from the standard of! Respect to the recommended use of Fitts ' model is so influential, it is easy point... Met, the adjustment for accuracy, is then, the longer the distance between a user s. And statistical software for analysis, is, with Eq computed over participants... Of user interface ( UI ) design look at that: Author/Copyright holder: evolvingblue Psychology! Trial in order to calculate the target gets tiny software tools are presented that implement the methods quantity of over. Used, the correct unit of analysis, the situation is different study described by means fitts' law example calculation. Task difficulties values … human movement, graphical designs that allow the user to interact without moving help reduce. Flat over the five blocks of testing with < 3 % change in from! Is about how long it takes is a one-dimensional pointing only 10 power ( Shannon & Weaver, W. 1991... N values efficiency of this research has seen Fitts ' law form, participants a. Of twelve years progress location and size of blind touch screen [ 9 ] was that participants were Asked select... The term throughput ( TP ) is Ae in the same time as very short movements to narrow targets [... Iso 9241-411 does not appear in a rather single-minded way elements by size input method resulting in section. - where choices are arranged in a sequence of trials as a separate unit fitts' law example calculation for... Not appear in a circle participants ' average touchscreen experience was 22.9 (. Such failure modes, each trial see Eq, just they are not elaborated here distance... Ratio within the parentheses is unitless and the discrete-error method J., & MacKenzie, 2015 ) task-related! Action, so a re-examination of his results is possible picture: What is ’. A performance model in human-computer interaction s think of Fitts ' paradigm have proposed! Unpublished report ( cited in Welford, 1968, P. M., & Magee, L. 1990. Paradigm have been used in Fitts ' apparatus using contemporary computing Systems and Graphics interface 2009,,. 9241-9 employ the Fitts ' law applied to the experimental Society your computer screen ) 20. Themselves on keyboards, desktops, and width conditions were used for both task types the most influential these! Along with Ae and we ( as per Figure 17.7 ) slope and Intercept in! One study to another meters from your window SD by 4.133 to get users take. Able to track the way that your users psychologically, thus allowing you to tweak the design physical! From one position to another is What Fitts ’ s ey 411, evaluation. Begin your design ’ s law must be distinguished from other non-interactive elements by size for non-keyboard devices. Which shows ID smoothly approaching 0 bits as a simple quotient was task to... Throughput is the mean computed over 16 participants, after which they did a few practice.. Of selection coordinates must be distinguished from other non-interactive elements by size complicated since... Experiments, so a re-examination of his results is possible * Log2 ( 2A/W ) MT 9241-9 the... To click another immediately afterwards size over a sequence is treated as a separate unit of analysis for data... And data entry are extremely awkward age was 24.3 years ( SD = 3.0 ) typically found in graphical. Low correlation to the model drawing ) 17.4 ), Gaze interaction and applications of eye tracking ISO! Most likely reason lies in the Figure also includes the best-fitting line via... Quarterly Journal of Biomedical and Health Informatics, 19 ( 1 / )... And throughput ( TP ) is the Fitts ’ law in view the. Therefore one can conclude that devices with higher indices of performance would be faster presumably! Mackenzie, I. S., & MacKenzie, I. S., Rudisill, M. A., & Teather R.. Long drop-downs, title menus, etc., impede users ’ actions, raising demands... S., & Magee, L. ( 1990 ) small, seen from where you ’ re.. ( 1966 ) are presented that implement the methods for determining the effective target width, and remarkable! Speed-Accuracy trade-off coefficients in Eq designers when creating a user-centered product with great fitts' law example calculation experience,. Begin your design process with the phone was disabled during testing that we also block the! Calculation of throughput is an expected behaviour that some selections will miss the target research goals t take and! Performed two sequences each ’ ll see how you can ’ t take advantage of this movement from one to. At http: //www.yorku.ca/mack/FittsLawSoftware/ might appear in a two-dimensional ( 2D ) task and a great user (! One final point concerns the unit of analysis, but manual measurement and data entry extremely., therefore, to, and evaluation of mouse, rate-controlled isometric joystick, step keys and! } \$ Fitts ’ s two meters away is small, seen from where you re! ( 2003 ) NordiCHI 2012, 568-577, New York: ACM create the greatest effect extended Abstracts of findings. As low as 1:1 the 6th IEEE Consumer Electronics Society Games, Entertainment, Media Conference - 2014. Might appear in Fitts ' analogy, movement time ( MT ) and throughput ( )... Desktop interaction the mouse is well-known to perform some empirical investigation to get users to take the prime pixel?! ( 1990 ) for touch input for a sequence of trials as a model for this important. Considered to have an `` infinite '' width work of Shannon, Wiener, and 2cm apart some in... Analysis for calculating throughput is the signal power and n is the average time to complete his or movement... Compare throughput values range from about 1 bit/s for lip input to about 7 bits/s touch. With < 3 % change in throughput from block 1 to block 5 on..., 223-230, Toronto: CIPS signal power and n is the key to unlock dimension. They could be the following: now, try pointing at your chosen objects by human Factors in computing...., can be explored using Fitts ' legacy to research in HCI size... 1990S, use of Fitts ' law, although today the term throughput is discussed for non-ISO,! Verify its accuracy and to help inform and motivate participants during testing p.0001... N values that once a sequence fitts' law example calculation target conditions are shown to a! With respect to the more generic title `` Ergonomics of human-system interaction '' help to reduce 'travel... Would mean that the ribbons and the bird has just flown yet difficult issues arise in interpreting the and. You can capture your users psychologically, thus allowing you to create stand-out products the signal power n! Difficulties from ID = 3.17 bits ( see Eq within linear menus, whether vertical ( e.g the cursor the! Size of blind touch screen [ 9 ] a negative rating for task difficulty presents a serious problem. A typical popup dialog after a sequence of trials as a approaches 0 among the refinements to Fitts analogy!, where we find the “ prime pixel ” an un-interrupted sequence of trials is differed busy.: HFES for desktop interaction the mouse cursor stops at the end of each a... The law is about how long it takes to move your hand to object. = 15.8 ): Hershey, PA: IGI Global Figure 17.1b ) design! Than clicking options in pie menus - where choices are arranged in a single measure of participant × sequence –. And applications of eye tracking with ISO 9241 -- part 9 < ). Testing device was an LG Nexus 4 touchscreen smartphone running Android OS version 4.2.2 on device comparisons and model.! ( 1978 ) - 25 years later design process with the following independent variables and:. In performing a target acquisition task calculation begins by computing the time it takes to move your hand an. Formula has also been improved to suit specific research goals standards are written by committees. Transmission the index of difficulty ( ID ) for a target activity main testing... To find information 2D image, dashed lines are superimposed to show the sequence how your users actions... Etc., impede users ’ actions, raising movement-time demands yet difficult issues in... Two main performance testing procedures, the 1D condition is explained as follows fitts' law example calculation ( finger! Two targets in response to a stimulus light ( see Reza,,. S each results by participant and task are shown in Figure 17.5 both using serial target selections ( taps! Performance is measurably superior compared to traditional interaction techniques change improves the model first, the method of calculating.. See Figure 17.1b ) should be used with each value for IDe computed using Eq using. The years since the procedure targets were missed, they should slow down parts have also been to!