Models and Theories in Human-Computer Interaction/Fitts' Law in Entry-Based Systems

Fitts' Law in Entry Based Systems (Briana Bettin)
Carroll's book "HCI Models, Theories, and Frameworks: Toward a Multidisciplinary Science points out how Fitts' Law was initially developed on larger scale areas of movement, where of course time between motions may be critical. While on a smartphone these movements may be marginally different (the difference from top to bottom of screen versus top to middle of screen may be only a fraction of a second, for example), the addition of time in motions can come to light very strongly in data entry based systems, where each movement matters and total delays count against production throughput.

When Every Keystroke Counts
An adage in data entry based jobs is "fingers never leave the keyboard". While for many of us it might be commonplace to use our mouse to move to the action we want to do on the screen, many times data-entry based jobs are trained for maximum efficiency at typing, meaning the ability to tab through and use "Enter" instead of clicking on forms is a must. This is in part likely due to Fitts' Law. The time it would take a data entry person to move their hands from the keyboard to the mouse, then to the button or field they wish to work with, then back to the keyboard to type significantly reduces performance in an eight hour day if they are entering hundreds of items in that day.

Say in theory moving your hands from your keyboard to the mouse takes 1 second, then 2 seconds to move the mouse and click the item you are looking for, 1 second back, and you must do this say, twice in each data entry. That's 8 seconds for every entry, and if you are doing 500 entries in a day, that's 4000 seconds, or about 67 minutes - a full hour added simply in movement back and forth. Pressing a key from standard keyboard hand positioning on the other hand, may take only .5 seconds, and using tab and enter keys for field movement and "clicking" significantly reduces the amount of hang time - this is why many data entry systems are designed as tab-able forms for maximum efficiency. In work where making the most of time matters, finding ways to optimize movement time between process steps is critical.

Keeping a Well Oiled Machine
Machine displays can be very similar in their necessity for ease of use within a maximized range. Typically a machine display in a factory gives diagnostics on the machine, or can be used to change settings such as mold type or conveyor speed. As factories rely on good production numbers to meet goals, it's essential that operators are able to utilize the machine's displays functionally while also working with the items coming off the machine - such as packing or assembling them.

Machine displays are very interesting as they require a removal and then reintroduction to the environment. A machine operator may not interact with the machine display for hours at a time, but when they must resolve an issue or change settings, they need to be able to do so as efficiently as possible to keep their lines moving. This is why it's critical that machine displays not only have buttons that from the display are easily reachable and usable, but also that the displays themselves follow Fitts' Law in placement relative to the active working station. If workers are typically moving between the conveyor and the boxing area, an ideal location for the display panel may be between these two spots to ensure no matter which job an operator is running at the time they need to access the panel, they are able to get to the panel in the same relative amount of time.

Efficient Systems, Efficient Workers
While many systems and interfaces utilize several other theories to ensure maximum usability for each user (and the ones above are no different in likely needing many other systems to ensure they are logical), systems where time and accuracy are of value can benefit greatly from utilizing Fitts' Law to ensure properly trained operators are able to work at the most effective capacity and create greater turnaround for the company as a whole.

Works Cited

Carroll, J. M. (2003). HCI Models, Theories, and Frameworks. San Francisco: Morgan Kaufmann Publishers.