We all know the paper towel dispensers that you crank to get the required length out. The more sophisticated ones dispense with the crank action and use an electric motor actuated by a proximity detector: wave your hand in the air in front of the machine and out comes the preset length of paper with a satisfying whirring sound. Hygienic, neat, and foolproof.

Two paper towel dispensers

But even with this foolproof concept there are different designs. The device at the left in the photo tells you to wave your hand to the right of the paper outlet slot. The one at the right has the sensor centered above the slot’s middle. Why does this matter? because the average person will reach out for where the paper is expected; with the second unit this will trigger the sensor, whereas with the first, it will not. Then you have to start groping and try to figure it out, and maybe notice the frantic effort the vendor made to guide you: the picture of a hand titled “sensor”, the big blue arrow pointing to it, and the text captions that try to make it all clear.

Towel Dispenser markup

All nice and good, but a towel dispenser is not a literary work, and should not rely on texts and explanations. Had they put the sensor in the middle all this would’ve been unnecessary…