Five Design Factors that Influence Speed

As I noted in a previous tip, there are typically a host of factors that affect speed, and the number of required button presses is just one of them. Many of these factors are outside of the designer's control. For instance, average transaction speed might be affected by the physical layout of the store, the process of getting customers through the line, the manager's communicated expectations, and much more. But these are usually beyond the purview of the user interface designer.

However, there's a lot the designer can do to help increase speed. Below, I've outlined a few aspects of a usable point of sale which designers should consider if increased speed is a requirement of the design:

  1. Hand movement. Obviously, the closer two points are to each other, the shorter time it takes to get from one to the other. A usable POS design will capitalize on this fact by ensuring that the most common tasks require the least movement. User interface designers should also consider the direction of motion when supporting such tasks, ensuring that there are as few changes in direction as possible.
  2. Button size and spacing. Buttons that are two small or two close together can reduce speed since users have to slow down to ensure they are hitting the right one. It's also helpful to remember that button size is not an absolute concept but is relative to the direction of hand motion. So, buttons that are longer than they are wide will be easier to hit if the hand is moving horizontally rather than vertically.
  3. Accessibility of commonly needed options. Buttons that are surrounded on all sides take longer to hit than those that have one or more sides free. This, along with visibility, is why user interface designers should try to put the most commonly needed options at the tops, edges, and bottoms of lists and groups.
  4. Logical organization. Sometimes, ordering and grouping things in logical ways trumps the "Accessibility Rule" (see #3). For instance, rather than move the "Medium Drink" button to the top of a list, it might be more important to keep it between "Small" and "Large", even if it is more commonly selected than the other sizes. Designers must know when—and to what extent—to apply these and other rules in order to optimally achieve the desired outcomes.
  5. Shortcuts. Another way to help increase speed is to design the Point of Sale system so it will allow the user to get faster as they become more experienced, as I've described in another tip (see Growing With the User).

These are just some of the ways to help increase speed. Typically, research with individual clients will reveal additional and more specific ways to achieve significant speed gains.