Laws that govern usability and pragmatic usage

Fitts' law

Fitts' law is quite intuitive, even a toddler knows that, you always go for the largest cookie/candy/cake/blah-blah...; even when it doesn't fit in the mouth. Might be the evolutionary instinct to pick up the most healthy objects! Well human vision can broadly perceive two kinds of visual inputs. Our brains are fine tuned to focus (a predatory trait), when we do that our peripheral vision takes a back seat. Then we do have peripheral vision, which kicks in autonomic-ally; more like a gag reflex. Like seeing a car coming or ball being passed from the back of your eye. Practice can enhance these traits, an archer would focus where as a ping-pong player relies on the lateral part.

Reading involves focus, so when someone looks at the screen, s/he immediately feels an urge to know what's around. So any attention grabbing activity attracts attention. The essence of this rule is simple, try to keep things together and highlight the action arena by making it big and closer to points in focus. Also, avoid placing unwanted focus-grabbers (remember lack of annoyances). Areas of application: Buttons, Labels, images, check boxes and radio buttons and almost every thinkable UI component that supports mouse activity.

Steerings' Law

Fitts' law highlights the point and click activity, Steerings' law extrapolates it to 'drag/draw' action. Wondering about things that fit into this? Stylus and tablets and pens and laser-pointers and touch-screens and pinch gestures WHOA... never thought of this before. On a typical application, you tend to use scroll-bars which `were` bad-ass as per this rule, (no wonder eldery folks hate UI). Try to customize the scrollbar, even more problems, people who have learnt UI rarely recognize the customized scrollbars. Now you have two problems. The you may have cross-browser issues (hundred's of problems).

So why are we even discussing this. Some widgets are not that popular and can benefit from steering's law. For example, most image-editing apps have a palette, It is customary nowadays to enable drag and drop on palette contents (point-click-relax and point-click-relax vs. point-click-drag-relax with focus thrown somewhere in between). Every such widget needs to support margin of motion. The user should never be constricted to a specific area.

On a side note: How to improve scroll bar? Add a on-hover effect which enlarges the scroll bar making it easier to click.


Crossing action is rarely seen supported in most UI applications, so we will put is aside for the time being.