Here's a great example of designing something for an impaired population, and making an improvement that benefits all. Mastercard has redesigned their debit, credit and pre-paid cards with different physical notches in them—round, trapezoidal and checkmark-shaped—so that the visually impaired can distinguish them by touch.
The additional benefit, of course, is that everyone will be able to use the off-center notches to accurately orient the cards, by touch, when inserting them into a machine.
I'd like to see a little more differentiation between the shapes, but I guess there's only so far they can take it with the material.
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