For most pointing devices, Paul Fitts's law can be used to predict the speed with which users can point at a given target position.

The circular menu slices are large in size and near the pointer for fast interaction ( see Fitts's law ).

Fitts ' law ( often cited as Fitts's law ) is a model of human movement primarily used in human – computer interaction and ergonomics that predicts that the time required to rapidly move to a target area is a function of the distance to the target and the size of the target.

Fitts's law has been formulated mathematically in several different ways.

Fitts's law is an unusually successful and well-studied model.

Experiments that reproduce Fitts's results and / or that demonstrate the applicability of Fitts's law in somewhat different situations are not difficult to perform.

The first HCI application of Fitts's law was by Card, English, and Burr ( 1978 ), who used the index of performance ( IP ), defined as, to compare performance of different input devices, with the mouse coming out on top.

Fitts's law has been shown to apply under a variety of conditions, with many different limbs ( hands, feet, head-mounted sights, eye gaze ), manipulanda ( input devices ), physical environments ( including underwater ), and user populations ( young, old, special educational needs, and drugged participants ).

Since the advent of graphical user interfaces, Fitts's law has been applied to tasks where the user must position a mouse cursor over an on-screen target, such as a button or other widget.

Fitts's law models both point-and-click and drag-and-drop actions.

Fitts's law has also been shown to model target-directed hand and head motions in a virtual environment.

* It describes untrained movements, not movements that are executed after months or years of practice ( though some argue that Fitts's law models behaviour that is so low level that extensive training doesn't make much difference ).

Fitts's law remains one of the few hard, reliable human – computer interaction predictive models, joined more recently by the Accot-Zhai steering law, which is derived from Fitts's law.

The logarithm in Fitts's law is called the index of difficulty ID for the target, and has units of bits.

Fitts's law can be derived from various models of motion.

Although this model is overly simple, it provides some intuition for Fitts's law.

# REDIRECT Fitts's law

The factor of 2 here is not particularly important ; this form of the ID can be rewritten with the factor of 2 absorbed as changes in the constants a, b. The "+ 1 " in the Shannon form, however, does make it different from Fitts's original form, especially for low values of the ratio D / W.

Hick's Law is similar in form to Fitts's law.

Fitts's law can be used to quantify the time required to perform a point-and-click action.

Early Apple experiments in GUI design initially used multiple menu bars anchored to the tops of windows, but this was quickly dropped in favor of the current arrangement, as it proved slower to use ( in accordance with Fitts's law ).

He developed a model of human movement, Fitts's law, based on rapid, aimed movement, which went on to become one of the most highly successful and well studied mathematical models of human motion.

* Visualizing Fitts's Law by Kevin Hale

Within human-computer interaction, the law was rediscovered by Johnny Accot and Shumin Zhai, who mathematically derived it in a novel way from Fitts's law using integral calculus, experimentally verified it for a class of tasks, and developed the most general mathematical statement of it.

At PARC his " study of input devices led to the Fitts's Law characterization of the mouse and was a major factor leading to the mouse's commercial introduction by Xerox ".

oriented perpendicular to the axis of motion ) can be modeled with this form of Fitts's law:

However, Bruce Tognazzini, former employee of Apple Inc. and human computer interaction professional, claims that the Mac OS's menu bars can be accessed up to five times faster due to Fitts's law: because the menu bar lies on a screen edge, it effectively has an infinite height — Mac users can just " throw " their mouse pointers toward the top of the screen with the assurance that it will never overshoot the menu bar and disappear.

With the release of Windows XP, Microsoft changed the behavior of the taskbar to take advantage of Fitts's law.

Some consider this a testament to the robustness of Fitts's law.

We see, especially in this simplified form, a speed-accuracy tradeoff, somewhat similar to that in Fitts's law.

It became the sole `` subject '' of `` international law '' ( a term which, it is pertinent to remember, was coined by Bentham ), a body of legal principle which by and large was made up of what Western nations could do in the world arena.

The enormous changes in world politics have, however, thrown it into confusion, so much so that it is safe to say that all international law is now in need of reexamination and clarification in light of the social conditions of the present era.

To him, law is the command of the sovereign ( the English monarch ) who personifies the power of the nation, while sovereignty is the power to make law -- i.e., to prevail over internal groups and to be free from the commands of other sovereigns in other nations.

Moreover, the law of the land is not irrevocable ; ;

That is to say Gabriel's fundamental law had been so much modified by this time that it was neither fundamental nor law any more.

It is a weakness of Gabriel's analysis that he never seems to realize that his so-called fundamental law had already been cut loose from its foundations when it was adapted to democracy.

Mr. Stavropoulos is the U.N. legal chief and a very good man, but he is not fully versed on some technical points of American law ''.

His father was a professor at Hartford Theological Seminary, and from him he acquired a conviction, which he passed along to me, that there is in the universe of persons a moral law, the law of love, which is a natural law in the same sense as is the physical law.

A careful student has suggested that `` In any new revision ( of the Judicial Code ) the legislators would do well to remember that the allocation of power to the federal courts should be limited to those matters in which their expertise in federal law might be used, leaving to the state judiciaries the primary obligation of pronouncing state law ''.

Mr. Justice Black led a reversing majority: `` Strict local rules of pleading cannot be used to impose unnecessary burdens upon rights of recovery authorized by federal law ''.

By ancient common law it might be required of all persons above the age of 12, and it was repeatedly used as a test for the disaffected.

In 1805, English instructor and natural philosopher John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers ( the law of multiple proportions ) and why certain gases dissolved better in water than others.

The term may be also used loosely or metaphorically to denote highly skilled people in any non -" art " activities, as well — law, medicine, mechanics, or mathematics, for example.

With regard to historic properties ( those properties that are listed or that are eligible for listing in the National Register of Historic Places, or properties designated as historic under State or local law ), those facilities must still comply with the provisions of Title III of the ADA to the " maximum extent feasible " but if following the usual standards would " threaten to destroy the historic significance of a feature of the building " then alternative standards may be used.

There is one test based on " Brazil law twinning " ( a form of quartz twinning where right and left hand quartz structures are combined in a single crystal ) which can be used to identify synthetic amethyst rather easily.

Some jurisdictions allow force to be used in defense of property, to prevent damage either in its own right, or under one or both of the preceding classes of defense in that a threat or attempt to damage property might be considered a crime ( in English law, under s5 Criminal Damage Act 1971 it may be argued that the defendant has a lawful excuse to damaging property during the defense and a defense under s3 Criminal Law Act 1967 ) subject to the need to deter vigilantes and excessive self-help.

There is no distinction made in Scotland between assault and battery ( which is not a term used in Scots law ), although, as in England and Wales, assault can be occasioned without a physical attack on another's person, as demonstrated in Atkinson v. HM Advocate wherein the accused was found guilty of assaulting a shop assistant by simply jumping over a counter wearing a ski mask.

Amdahl's law, also known as Amdahl's argument, is named after computer architect Gene Amdahl, and is used to find the maximum expected improvement to an overall system when only part of the system is improved.

P estimated in this way can then be used in Amdahl's law to predict speedup for a different number of processors.

* Adjusted winner procedure, a procedure used in fair division law

Arbitration is also used by communities which lack formal law, as a substitute for formal law.

On the continent of Europe among some civil law systems ( i. e. those deriving from Roman law or the Napoleonic Code ), the inquisitorial system may be used for some types of cases.

The ideal gas law or another equation of state is often used in conjunction with these equations to form a determined system to solve for the unknown variables.

Regulatory Arbitrage was used for the first time in 2005 when it was applied by Scott V. Simpson, a partner at law firm Skadden, Arps, to refer to a new defence tactic in hostile mergers and acquisitions where differing takeover regimes in deals involving multi-jurisdictions are exploited to the advantage of a target company under threat.

The term " black-letter law " is also used commonly in the American legal system to mean well-established case law.

In English law, black letter law is a term used to describe those areas of law characterized by technical rules, rather than those areas of law characterized by having a more conceptual basis.