I am left-handed, which means that I have many more opportunities than 90% of the population to appreciate the complexities of interacting with everyday objects. Left-handers are often acutely aware of the design of scissors, desks in large lecture halls, spiral-bound notebooks, and fountain pens, just to mention a few objects associated with an educational environment. These are ordinary hurdles that most left-handers have become familiar with (specifically, using scissors left-handed tends to force the closing blades away from each other, and are uncomfortable besides; most small folding desktops are designed for writing on the right side; the wire of a spiral-bound notebook digs into the left hand doing the writing; pushing a fountain pen left-to-right with the left hand, rather than pulling with the right, causes the nib to spread--don't even ask about the smearing that results.) I recently ran into unexpected difficulties with a vending machine, however, which caught me by surprise.

This vending machine stands in the corner of a large undergraduate common room, behind a door that is always propped open. The coin slot is on the right hand side, which puts it close to the wall, near the hinges of the door.

I usually carry change in my right pants pocket. This is not out of any forethought, but rather the result of holding a handful of change in my right hand and picking out the appropriate with my dominant left hand. When buying a drink from this vending machine, then, here's the procedure: I sidle behind the door to the front of the machine. I pull out my change with my right hand and pick out a quarter with my left. I reach out to insert the coin in the slot. . . And here I run into trouble. The coin slot is built into a panel that's recessed into the machine (to give full prominence to the advertising across the front of the machine.) The knuckles of my left hand, holding the quarter, bang right up against the edge of the advertising, so that the coin just barely can't reach the slot. I can't back up--the propped-open door is in the way. I can't move to the right for more room--the vending machine is right up against the wall. There's not even enough room to pour the coins from one hand into the other. Instead, I step sideways out from behind the door, transfer the coins to my left hand, and then back in to insert them with my right hand into the machine. Sound silly? It certainly has seemed so to the students who have observed my little dance. Nowadays, when I remember, I put my change in the correct hand, or I close the door before using the machine.

Can this tell us anything about design? One message is that designers (even those whose design responsibility extends no further than placing large machines against specific walls) must be aware of variation in their user population. It's sometimes tempting to build a solution for a problem that is well-suited to the "average" user. But this is very often inadequate. Imagine that we're designing a chair to be used by the "average" person in the average household in the U.S. We'd take the heights of an adult male, an adult female, and 2.4 children, giving an average height of perhaps 4.5 feet. . . Already it's clear that we've done something wrong. Instead of targeting some hypothetical ideal individual, we expand our view to either everyone who might use our design or some significant subset of this population. For example, we might say that our chair should be comfortable for everyone from the 5th to the 95th percentile in height (along with whatever body part proportions and weight factors we think are relevant.)

There are other relevant design issues that we might consider here, such as physical constraints (imagine the difficulties a disabled person runs into every day), but I'll save those for another essay.