multi-use physical buttons

Question

The company I work for is beginning to incorporate LCD screens onto its devices, but not touch screens. These machines will be used in dirty, dangerous environments, so touch screens are not practical.

For cost and space reasons, one particular device can only have a max of 4 buttons. However, they want the user to be able to store 8 different settings in the memory. They're proposing something like this (colors and fonts changed for anonymity).

Each button would hold two memories, and you would switch between the two by pushing the button twice. You tell which memory you're in by which side the light is on. In the picture, you would be in Memory 2, because the light is on beside the 2.

My gut reaction is that the extra button presses and dual settings on each button make this a bad UI design. But does anyone have any research to back this up or refute this? Are there studies on this sort of behavior? Antecdotal findings? Or can this only be solved through testing? Thanks.

Answer 1

The above solution is absolutely more cumbersome to understand than an eight-button setup, and perhaps moreso than a selector button plus a 7-segment display showing which memory is being used. But it also might be suitable given your users, their tasks, and the work context.

A design is rarely "bad" or "good"; those are extremes that rarely exist in the real world. Thinking that way may prevent a team from working together to agree on a viable design. A design needs to be evaluated in the context of its use.

You're facing a tough constraint: fit eight memories in four buttons or less (plus, presumably, additional buttons for setting or recalling the memory slots). We don't know what other constraints you have, nor how negotiable those constraints are.

You might go back to the team and ask them important questions about the tasks like these:

• What is resulting in the 4-button limitation?
• What other widgets can we use? Can we use displays? Switches? Knobs?
• Do we know how many memory slots our users actually need, or expect?
• How frequently do users switch between memory slots?
• How frequently does a particular slot get used? Would it be okay to have fewer slots and an easier way to swap the contents of a slot?
• In a dangerous, dirty environment, will users be able to see the small lights beside each button?
• What sorts of interfaces are our users used to?
• Will this interface be used by novices, or can we reasonably expect the user to build up some knowledge of how to get things done?

These may help mitigate some of your concerns, and help you identify a solution that fits within your constraints.