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The Primary Interface

Worry about the most important job first. February 19, 2007 

Synopsis: I've noticed in several different UI situations that there' s a concept of "the primary interface" meaning the most basic, stripped down expectation of a user. For instance, for address signs it's the address. Well, duh!

I first noticed the concept of "the primary interface" on phones. Despite their getting more complex over the last 20 years, a residential or business phone should still respect the primary interface. This means that...

  • when it rings you should be able pick it up and talk, and
  • to make a call you should be able to pick it up, and dial.

Yes, we allow one exemption for the "Talk" button because of cordless phones, but that's it. All the bells-and-whistles shouldn't eliminate the operation of the primary interface.

I noticed the concept again at Home Depot, where I spend most of my life. The ACM (automated cashier machine) at Home Depot honors the primary interface as follows. Despite prompts for such things as "Language" and "Finished?" I can ignore every prompt and execute the following transaction:

  1. Walk up to it
  2. Scan my items
  3. Put in cash and leave (with or without my change).

At the grocery market, all sorts of extraneous prompts (Any Coupons? etc.,) prevent the primary interface, and you have to spend time learning how to use it. But now let's get on to today's example.

If you've made it this far, I have a free gift for the first 10 visitors who reply. If you know anyone who's learning to read, email me and I'll send you a free copy of a kid's book I wrote that has just been printed (February 14th, 2007). For smart mouths everywhere, the book is PoopyPhonics(.com). No strings attached, but if you like it, consider posting a review to Please include "Poopy Phonics" in the subject line so I have a chance of recovering it if it goes to my spam folder. —Thanks, Jack

—No spam, no emails, no private info given out—


You're driving down Swedesford Road. It's a 5 lane road and the speed limit is 45, so the traffic is moving 55-60. You are looking for 565 Swedesford. It so happens that 575 does have 4-foot tall letters saying '575,' but they're at the top of the dark brown brick building... and they're a nice dark brown color themselves! No one sees them, so drivers are left to spot the address on this sign:


Across the street they must have left this decision to a person who was paying attention:

Mind you, these signs existed first. So this before-and-after is basically over.

For the diplomatic, constructive, philosophical version of this post, um... um... I'm not sure what to tell you. I guess I could plumb the shallows of the business world to try to explain how it is that a non-designer makes such a design decision, but what's the point?

"My interest in usability arose from the pain and tears of patching the wounds of suffering interface designs with the inadequate bandages of help files and user guides." — Daniel Cohen

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