Monday, March 11, 2013

Number of States in Credit-Card Swiping

When I am shopping and I slide my credit card incorrectly, it is common for a store employee to tell me to swipe the card "the other way". I am very confused by this statement (and, especially, the sense of obviousness that I am apparently supposed to feel but which I fundamentally don't), as there are clearly four different ways of swiping a card based on orientation alone because one can flip the card via either the vertical or horizontal axis. And to get only four different ways, one is already assuming that swiping forwards and swiping backwards is the same and that issues like adiabaticity versus non-adiabaticity of the swiping also don't matter. (The number of states is arguably uncountably infinite if one takes the latter into account.) I am willing to make those assumptions in the count of the number of ways to swipe, but this still yields four possible orientations for the card---so I just don't understand the comment of "the" other way that I have now received from numerous people. My usual response goes something along the lines of "Which other way? There are four in total. I have no way which of the other three ways you mean." tends to be met with a look that I can only describe as a mixture of confusion and pity. I am not doing this to be a pain in the ass---I really can't tell which of the three they mean!


Unknown said...

You can reduce the possible states to 2 by noting that the magnetic strip on the credit card needs to be inside the machine when you swipe. If the strip isn't visible, just remember it's always on the top half of the card.

Mason said...

Having to remember things is never a good sign.