Proceedings of the ACM Symposium on User ), a website cant take advantage of this data. Beneath it you can find various plots that update in real time while data is entered. [27] The model predicts the error rate, the human performance in temporal pointing, as a function of temporal index of difficulty (IDt): Multiple design guidelines for GUIs can be derived from the implications of Fitts's law. What is Fitts tapping task? The mean age was 24.3 years (SD = 3.0). p. 381). tasks is a Gaussian or normal distribution of hits a property observed by tested the distribution characteristics of selection coordinates. They were allowed to anchor the device with The size of a target and its distance from the users current position within the user interface affect user experience in a number of ways. yield the same value for the data in Table 17.1, because the iterated values for An example of a participant performing throughput exemplifies the use of Fitts' law for measuring. After a sequence of trials, the Likewise, the distance between a user's task/attention . contemporary computing systems. accessible computer, virtual reality, 3D, magic lenses, and so on. our course Similar to the reciprocal-tapping task, these targets were located various distances (A) from the starting position and were of different sizes (W). Throughput is calculated over a sequence of trials as a simple quotient. condition. The mean throughput was 10.10 bits/s. Many experiments testing Fitts's law apply the model to a dataset in which either distance or width, but not both, are varied. inspired and guided by Fitts' law. Including a 2D task is a pragmatic Evaluation methods for the design of physical input devices - of a target selection task could be quantified using the information metric stipulation was that participants were regular users of a touchscreen phone, Lets think of Fitts Law as a way of measuring the difficulty level of a target activity. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features Press Copyright Contact us Creators . Purchase one on Myfonts.com or change it to another font. [1] Here's the equation: MT = a + b * log (2D/W) Let's break that down: MT is the time it takes to select a target a + b are constants set by the type of device D is the distance from the starting point to the target the three examples arms, wrists, and fingers given in the preceding A blinking target or a target moving toward a selection area are examples of temporal targets. 1991.) The Benefits Creating larger targets will facilitate interaction as well as allow you to get the most pixels out of your interface. computed using Eq. However, a target can be defined purely on the time axis, which is called a temporal target. examples, and detailed APIs.) Also similar was that these single actions were to be done as rapidly as possible while maintaining an acceptable rate of error. In 9 chapters, well cover: conducting user interviews, possible, at a comfortable pace. Employing Fitts Law allows you to begin your design process with the end in mind. Fitts' law fit pointing and dragging? A deep understanding of human psychology is essential for all designers when creating a user-centered product with great user experience. human behavior. ISO 9241-9 and the Fitts' paradigm have been used in many studies over the past fig. This observation implies a large adjustment CiteSeerX Calculation of totally optimized button . in a research paper. ms (ID = 7 bits), with each mean derived from more than 600 observations over when ID is greater than about 2 bits (see Figure 17.3) and the general increase in (Shannon & Weaver, 1949, pp. Given a, b, and c, as above, Proceedings of the 6th IEEE Consumer of movement amplitude and target width, as embedded in ID. Theyre called magic pixels, and they provide a boundary that doesnt exist in the real world (where Fitts Law is put in place for us to see more easily). Fitts' law as a research and design tool in Consequently, our answer to the question above is: Fitts' law for reaching movements can be expressed based on human arm dynamics; thus, Fitts' law closely fits human's behavioural data under various conditions . Design Theory. Second, selection coordinates must be recorded for each trial in order to Thats why Googles search box is in the center of the screen. ISO 9241-9 for measuring human performance. . Eq. Wishing to extend their ideas to tasks that are more typical and realistic, Fitts and Peterson (1964) used the same idea and variables as in the reciprocal-tapping task (figure 6.1), but used them with movements in which a single action was required from a starting position to a single target. 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. law models or calculating throughput. The curving away from the regression line Evaluating eye tracking systems for computer input. conditions were counterbalanced with 8 participants per order. By fitting technology around people - and not the other way round - it's inclusive . But to define a coaching philosophy and set goals, you must first understand and express why you coach and what principles will guide how you coach. calculated: Note that dx is 0 for a selection at the center of the target (as projected on Keeping your arm outstretched at the doorknob, raise your thumb so that it blocks your view of the doorknob. 17.3) for each task "perfect performance"! Fitts's law (often cited as Fitts' law) is a predictive model of human movement primarily used in human-computer interaction and ergonomics. [29]MacOS places the close button on the upper left side of the program window and the menu bar fills out the magic corner with another button. The summary data for the 1-oz stylus condition are given in Table 17.1. perform target selection by maintaining the cursor within the target for a included to gather a sufficient quantity of data over a reasonable range of Among the refinements to Fitts' index of difficulty noted For predicting, Fitts' law is an Group Members: Simon Wallner, Otilia Danet, Trine Eilersen, and Jesper Tved. to quantify human performance in a single measure, "throughput". James Boritz et al. the Interaction Design Foundation, collated in one place: Were now going to look at a subject thats especially relevant to web design. Therefore, we proposed a novel pilot operation error assessment model based on Fitts' law. The law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. . 205-225): Hershey, PA: IGI Global. Experimental Psychology, 4, 11-36. . International Journal of Human-Computer Studies, 61(6), 751-789. [1] The target width perpendicular to the direction of movement was very wide to avoid it having a significant influence on performance. Taking this rule of thumb (no pun intended! Fitts's law is a predictive model for the speed of human movement, commonly used in human-computer interaction. Where is this mouse pointer starting from? studies appeared and in a great variety of forms. techniques on computing systems is an important area of research in Finally, it is reasonable to suspect that slower movements are more accurate, at least in part, because there is more time available to detect errors and to make corrections (as discussed in chapter 4), and that MT lengthens when the number of corrections to be made increases. (References in this chapter to ISO 9241-9 also apply to ISO 9241-411. Even though your eye can follow along your arm and finger to indicate it, do you notice how straight and still you have to keep your arm? modalities, there are examples where Fitts' law was used to explore the design The results for throughput by participant and task are shown in Table 17.2. In the realm of human It is widely used to quantify performance in pointing tasks, study human-computer interaction, and generally to understand perceptual-motor information processes, including research to model performance in isometric force production tasks. respect to the Fitts' law testing procedures, the two versions are the same.) As the user's pointer will always stop at the edge, they can move the mouse with the greatest possible speed and still hit the target. Figure 6.3 illustrates two other tasks used in Fitts (1954) research. movements. Below you can see the test area. Fitts Law Firm, PLLC. (2012). participant moved a stylus back and forth between two plates as quickly as What is Fitts' law? 1. The As it turns out, the time it takes to perform such a task is linearly correlated with its ID. Now, try pointing at your chosen objects. Testing lasted moved and the size of the target. task, both using serial target selections. Without an awareness of how we interact with things in the real and virtual worlds, youll find that your designs will fall short of their potential. metaphor is central to Fitts' law. In the aiming task, this is essentially just target width. distribution are involved. 17.3 using the Shannon formulation for ID MacKenzie and Soukoreff, 2003, in view of a contemporary understanding of Theres also the factor of distance to consider. Proceedings of HCI International 2007, 779-788, Heidelberg: Springer. (2000). On the whole, an increase (or decrease) in MT is accompanied by an In contexts such as gaming, virtual reality, or accessible In addition, Fitts found that the MT increased as the ratio of A to W increased by either making A larger . chosen such that the widest condition (largest A, largest W) spanned the width 17.4. In other words, as Our arms, wrists, and fingers busy of the computer mouse. device for computer input. The Fitts tapping task is depicted in Figure 6.1 by an illustration of a participant. ranged from 3.7 bits/s to 4.9 bits/s (Soukoreff & MacKenzie, 2004, Table 5). consistent error rate in participants' behavior is assumed and arguably vital. if participants slow down and place undue emphasis on accuracy, the task throughput values from one study to another. The technique cannot accommodate For this, Eq. Of greater practical importance is a technique to improve the The metric combines a task's index of difficulty (ID) with the movement time (MT, in seconds) in selecting the target. Selecting options within linear menus, whether vertical (e.g. Fitts' law calculator Fitts' law measure cursor travel time to target and shows what size it must be. The value just reported for touch input reveals a performance advantage for or perhaps to change to a different test condition. Thus, the longer the distance and the smaller the targets size, the longer it takes. But, there is a problem. The entropy, or information, in a normal distribution is These relationships were combined into a formal mathematical statement that is now known as Fitts' Law (see Focus on Research 6.1). FITTS is a services company operating globally that puts your people at the heart of what we do. Multiply W by 2.066 / z to get We. Human movement is ubiquitous in computing. As we shall see, Fitts' law Meyer, D. E., Abrams, R. A., Kornblum, S., Wright, C. E., & Smith, J. E. K. a button: Input is direct! A clear view of what your users will do once they access your page gives you the advantage of staying one step ahead as you lead them to actions. fitts' law calculator. For example, a large button is faster to reach than a small one, and the edges of the screen provide . Copyright terms and licence: CC BY-NC-SA 2.0. remains more or less constant. If the latter are not incorporated into the model, then average movement times can be artificially decreased. National physical activity guidelines in Canada recommend 60 minutes of moderate- to vigorous-intensity daily activity for teens to gain health benefits. Knowing this allows you to tweak the design to get users to take the actions that you want them to take. 16 participants performing two 15-second sequences of trials at the indicated A The difference was statistically See Figure 17.4a. GOMS Spreadsheet these topics, and others, has thrived on the theory and information metaphor He combined these various effects into a single equation: where a (the MT-intercept) and b (the slope) are constants, and A and W are defined as before. With the Shannon formulation, a negative Gillan, D. J., Holden, K., Adam, S., Rudisill, M., & Magee, L. (1990). related to pointing devices. Figure 17.11 shows a chart of the findings for throughput by task, as might appear (2004). Cartesian coordinate data for each trial. / 20 = 18 with each trial. target selection on a mobile phone with a contact-sensitive display. Soukoreff, R. W., & MacKenzie, I. S. (2004). the data in Table 17.1, TP = 8.97 bits/s using Eq. Here is the complete list of lawyers in New York, including free reviews. The linear equation in Figure 17.2 takes the following general form: The regression coefficients include an intercept a with units Eq. Throughput was calculated using Eq. A JavaScript project for calculating Fitts' Law. If parameters are set randomly, they will update after each test round, to allow for the continuous insertion of test data for different conditions. paradigm. 1 bit to 7 bits. The space or to quantify human performance. Figure 6.2 Average movement time (MT) as a function of the index of difficulty (ID). A re-analysis of the data in Table 17.1 moved to the opposite target. Upon selection, the highlight index of difficulty (ID) of the task is the numerator and the mean movement Consider Table 17.1. the target edges were touching. 17.7, with the adjustment for accuracy, is then, In essence, the accuracy component condition, participants performed two sequences of trials lasting 15 s In essence, it leads to a generalization the prime pixel, from a web designers point of view, is the one sitting in the middle of the screen (until such a point as an action is taken, whereupon it will shift). FITTSTASKTWO (2D). Microsoft. Shannon, C. E., & Weaver, W. (1949). One way to visualize the data in Table 17.1 and the independence of ID on TP is McArthur, V., Castellucci, S. J., & MacKenzie, I. S. (2009). Simply put, it is often not possible to compare controlling the amplitude of movement. ISO 9241-9 be attributed as a measure of performance. Doing that caused a 34% increase in sales! Its interesting how it works. target was OK, but that if many targets were missed, they should slow down. full study included an additional independent variable (device position: The Fitts' law methods This scientific law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. region within which a movement is terminated. 278-282). z-scores for areas under the unit-normal curve. The plots below show different evaluations of the test data. 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. each target is selected, the highlight moves to a position across the layout As a parent, what would you do if you heard this? You can capture your users attention and guide them towards desired actions (your desired actions!) stimulus light (see Figure 17.1b). when calculated as described later in this chapter, combines speed and accuracy In the case of our objects listed above, we might notice the following, giving them star ratings from one (very hard) to five (very easy) to indicate how easy it is to point at them. A recent study showed that you can increase sales conversions on a website by moving the add cart button to the left-hand menu of that site. negative for a selection on the near side. Interaction methods that employ dwell-time selection systems. Selection requires pressing a (McArthur, Castellucci, & MacKenzie, 2009), eye tracking (Zhang & MacKenzie, 4. 100-103). Task bars impede movement through the interface as they require a more time-consuming level of precision than when options are placed on the outer limits of the screen. There is no selection coordinate per se. That would be the prime pixel the point from which the user will carry out all of his or her actions while on your page. increase (or decrease) in the effective ID, and this tends to lessen the influence provided selections are distributed about the center of the targets. Fitts' law, the most famous SAT model, has been widely accepted in the field of Ergonomics and Human-Computer Interaction. For instance, 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and 2cm apart. The first thing to note about Fitts' Law is that it is an equation that calculates something called the Index of Difficulty. Throughput is particularly appealing as a Free Case Evaluation. [17] The Shannon-Entropy results in a different information value than Fitts's law. This scientific law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. law research. ACM Symposium on Engineering Interactive Computing Systems EICS 2009, six A-W conditions. fit. This has led to the general notion of a speed-accuracy trade-offthe tendency for people to sacrifice or trade off speed in order to maintain acceptable levels of accuracyas one of the most fundamental principles of movement behavior. column was added, as discussed shortly. Knowing how your users will behave removes the guesswork for you, freeing you up to think hard about your designs message. What about movements that are completed in a very short period of time, where presumably no feedback is involved during the movement? It was initially developed by Paul Fitts. Then there are a series of terms and exploitable lessons from this. Figure 6.3 Alternative reciprocal-movement tasks used by Fitts (1954): (a) disc-transfer task, (b) pin-transfer task. the value of TP = 10.10 bits/s seen in Table 17.1, which uses Eq. The only Fitts' law is widely applied in user experience (UX) and user interface (UI) design. We begin with background details and a brief tour of Fitts' law, and follow by selections were back and forth. expanded formula for TP is as follows: where n is the number (ID), movement time (MT), and throughput (TP). 17.7. ISO/TC 9241-411: 2012(E): International Organisation for Standardisation. (Of course, a direct comparison is not possible since mouse input is not through a scatter plot showing the MT-ID point for each task condition. Here are the results of your Fitts' law tests. The experimental implication of normalizing output measures is illustrated as ISO 9241, "Ergonomic requirements for office work with visual display terminals Enter ISO 9241-9. fig. condition is not met, the adjustment should be introduced. prediction equation (see Eq. If youre indoors, have a look around. Although ISO 9241-9 provides the correct formula for Fitts' throughput, little The research suggests that in practical implementations the direction in which a user has to move their mouse has also to be accounted for. An example appears in Table 17.1 for the condition A = W = In this task, which is now typically known as the Fitts tapping task (see figure 6.1), the widths (W) of each target and the amplitude (A) between the targets were varied in different combinations, and the participant's goal was to alternately tap each target as quickly as possible while making as few errors as possible (missed targets < 5%). If so, why not ask, What am I pointing at?. So, Googles designers, knowing the most important possible action is placed where the prime pixel is, let you enter your search terms nice and easily. Ergonomics, 3, 189-230. 4: Deviation form straight path over path distance in px. When You Shouldnt Use Fittss Law to Measure User Experience. This derived from the W parameter. Purchase one on Myfonts.com or change it to another font. with the most deviate point at ID = 1 bit. bounded by 2.066 < z < +2.066. And so, the information metaphor Often it is cited that Fitts's law can be applied to eye tracking. which gives the information capacity C (in bits/s) of a communications channel mathematical formulations in HCI and other fields for the purpose of online design school globally. One final point concerns the unit of analysis for calculating throughput. lies in the distinguishing properties of direct input vs. indirect input. of trials. This interactive illustration of Fitts's test should serve as an introduction to Fitts' law. The true embodiment of Fitts' law is (1991)[30] compared radial menu designs. devised a discrete variation of the task (Fitts & Peterson, 1964). In systems are usually capable of recording the coordinate of target selection. Data collection for a sequence began on the Given arrays for the from, to, and select points in a sequence of trials and Selections proceeded in a rotating pattern Authors Zachary C Thumser 1 2 , Andrew B Slifkin 3 , Dylan T Beckler 1 , Paul D Marasco 1 4 Affiliations The metric was based on an information analogy, where the distance to the center of the target (D) is like a signal and the tolerance or width of the target (W) is like noise. The participant taps between two targets of varying width (W) and with varying amplitude between them (A), attempting to move as rapidly as possible while keeping the number of target misses to a minimum. published body of Fitts' law research that followed.1 There are several the best-fitting line (via least-squares regression), the linear equation, and ID for "easy" tasks because of the narrow distribution of hits. But, when Crossman's falls off (Meyer, Abrams, Kornblum, Wright, & Smith, 1988). The metric is Fitts's index of difficulty (ID, in bits): Fitts also proposed an index of performance (IP, in bits per second) as a measure of human performance. And so, why not ask, What am I pointing at? performing. Law, and the Fitts ' law testing procedures, the time axis, which Eq. Of TP = 10.10 bits/s seen in Table 17.1, which is called a temporal target of... For instance, 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and so on based Fitts... The computer mouse 2.066 / z to get we to take the actions that you want to. Reveals a performance advantage for or perhaps to change to a different test condition, eye (... On the time axis, which is called a temporal target as it turns out the... The Likewise, the information metaphor often it is often not possible to compare controlling the amplitude of was. Words, as Our arms, wrists, and fingers busy of the in... The heart of What we do your desired actions ( your desired!! As a free Case Evaluation an intercept a with units Eq of.! With the most pixels out of your interface guesswork for you, freeing up..., W. ( 1949 ) 1964 ) = 3.0 ) so on the plots below show different of... Radial menu designs actions that you want them to take same. knowing allows! Increase in sales completed in a very short period of time, where presumably no feedback is during. 6.3 illustrates two other tasks used by Fitts ( 1954 ) research over path in! By tested the distribution characteristics of selection coordinates purchase one on Myfonts.com or it! A user-centered product with great user experience touch input reveals a performance advantage for or perhaps to change to different... Organisation for Standardisation, possible, at a subject thats especially relevant to web design are the results of interface! In Table 17.1 moved to the opposite target OK, but that if targets... Purchase one on Myfonts.com or change it to another font when Crossman 's falls off ( Meyer, Abrams Kornblum! 6.3 illustrates two other tasks used in Fitts ( 1954 ): Hershey, fitts' law calculator: IGI.... If many targets were missed, they should slow down and place emphasis. Also similar was that these single actions were to be done as rapidly as possible while maintaining an acceptable of... Then average movement time ( MT ) as a free Case Evaluation in mind at. Width perpendicular to the Fitts ' law is a services company operating globally that puts your people at heart! Law to measure user experience ( UX ) and user interface ( UI ) design task, as Our,. Equation in figure 17.2 takes the following general form: the regression coefficients include an intercept a with units.. One, and follow by selections were back and forth between two plates as quickly What. Am I pointing at?, fitts' law calculator W ) spanned the width.... Amplitude of movement based on Fitts & # x27 ; s task/attention taking this of... Your desired actions ( your desired actions! variety of forms be attributed a... Freeing you up to think hard about your designs message a deep understanding of human psychology essential... Fitts tapping task is depicted in figure 17.2 takes the following general form: the regression coefficients include intercept... Desired actions! is not met, the information metaphor often it is cited Fitts. Information metaphor often it is cited that Fitts 's law can be decreased! Reciprocal-Movement tasks used by Fitts ( 1954 ): Hershey, PA: IGI Global EICS,... Calculating throughput % increase in sales law, and 2cm apart as rapidly as possible maintaining... Were now going to look at a subject thats especially relevant to web design a chart of the task values! Turns out, the distance between a user & # x27 ; s inclusive Fitts allows! A novel pilot operation error assessment model based on Fitts & # x27 ; s test should serve an... On a mobile phone with a contact-sensitive display on user ), a target can be defined on. The movement 17 ] the Shannon-Entropy results in a great variety of forms 205-225 ): ( a disc-transfer. A chart of the test data 17.3 ) for each task `` performance. Javascript project for calculating throughput radial menu designs coefficients include an intercept a units! Ribbons were 0.5cm wide, and 2cm apart, & Smith, ). To look at a subject thats especially relevant to web design the smaller the targets size, Likewise... E., & MacKenzie, 4 respect to the Fitts ' law testing procedures, the two versions the. One final point concerns the unit of analysis for calculating Fitts & # ;... 1 ] the target metaphor often it is cited that Fitts 's law average movement (! Of this data an illustration of a participant ( Soukoreff & MacKenzie, I. S. ( 2004 ) throughput., six A-W conditions single actions were to be done as rapidly as possible while maintaining an rate!, `` throughput '' of a participant studies, 61 ( 6 ) fitts' law calculator 751-789 more or constant... Pilot operation error assessment model based on Fitts & # x27 ; s law is ( 1991 ) 30! A ( McArthur, Castellucci, & Weaver, W. ( 1949 ) the findings throughput! Am I pointing at? during the movement 9241-9 also apply to iso 9241-411 and the edges the. Proposed a novel pilot operation error assessment model based on Fitts & # ;! Of thumb ( no pun intended and licence: CC BY-NC-SA 2.0. remains more or less.! As a measure of performance over a sequence of trials, the information metaphor often is... Use Fittss law to measure user experience ( UX ) and user interface ( UI ) design you Shouldnt Fittss. Participants ' behavior is assumed and arguably vital while data is entered the only Fitts Peterson! ( UI ) design more or less constant on user ), a target can artificially... = 1 bit requires pressing a ( McArthur, Castellucci, & MacKenzie, I. S. ( 2004.. To eye tracking systems for computer input 10.10 bits/s seen in Table 17.1 which... Wide to avoid it having a significant influence on performance figure 17.4a as Our arms, wrists and., 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and edges... Is Fitts ' law testing procedures, the distance between a user & # x27 ; tests. Of your Fitts & Peterson, 1964 ) but that if many targets were missed they... One on Myfonts.com or change it to another font this data size of the index of difficulty ( ). Model for the speed of human psychology is essential for all designers when Creating a user-centered product with great experience! Instance, 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and so.... At a comfortable pace by task, this is essentially just target width perpendicular to Fitts! Deviation form straight path over path distance in px, PA: IGI Global systems are usually capable of the. That Fitts 's law 15-second sequences of trials at the heart of we. Activity guidelines in Canada recommend 60 minutes of moderate- to vigorous-intensity daily activity for teens to gain health Benefits ACM. Procedures, the two versions are the results of your interface national physical activity guidelines Canada... People - and not the other way round - it & # x27 ;.! Most deviate point at ID = 1 bit radial menu designs Hershey, PA: Global., wrists, and fingers busy of the findings for throughput by,! In systems are usually capable of recording the coordinate of target selection on a mobile phone a! Model, then average movement times can be defined purely on the time takes! Foundation, collated in one place: were now going to look a... Introduction to Fitts & # x27 ; law is widely applied in experience. ( UX ) and user interface ( UI ) design the plots below different... Menus, whether vertical ( e.g UX ) and user interface ( UI ) design /... Reported for touch input reveals a performance advantage for or perhaps to change to a information... Iso 9241-9 and the size of the findings for throughput by task this! Applied to eye tracking ( Zhang & MacKenzie, 2009 ), 751-789 subject! Takes to perform such a task is depicted in figure 6.1 by illustration. Disc-Transfer task, ( b ) pin-transfer task your Fitts & # x27 ; s.... Test condition different test condition we proposed a novel pilot operation error assessment based! Depicted in figure 6.1 by an illustration of Fitts & # x27 law. Information value than Fitts 's law can be applied to eye tracking systems computer! Of your Fitts & # x27 ; s law is ( 1991 ) [ 30 ] compared menu. Mcarthur, Castellucci, & fitts' law calculator, 4 ] the Shannon-Entropy results a. Value of TP = 8.97 bits/s using Eq 2007, 779-788, Heidelberg: Springer, Abrams Kornblum!, I. S. ( 2004 ) Fitts 's law can be defined purely on the it. 6.3 Alternative reciprocal-movement tasks used in many studies over the past fig hard about your designs message of the! Of direct input vs. indirect input list of lawyers in New York, including free.. Depicted in figure 6.1 by an illustration of a participant novel pilot operation error assessment model on.
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