Man, Magician, Machine

There are a lot of reasons to hate getting your hair cut when you’re a kid. Reason #1: sitting still sucks. Reason #2: Sharp scissors + ears = pain. Reason #3: it’s scary going to school with a new look, especially when that look is the result of a tearful afternoon spent with your mother and a pair of scissors, in which mom keeps muttering “oh, now that side’s shorter!” and, at the end of which you are told coaxingly that you look like Ramona Quimby, and “isn’t that fitting?”.

Before self-consciousness kicks in, I think Reasons #1 and 2 are enough to instill an early hatred of the barber shop. But this was not so for my siblings and I. When we were little and living in Ann Arbor—before the west coast, before the first grade, before my mother took the shears into her own hands*—we had Fantastic Sam’s. And Fantastic Sam’s meant magic.

The basic idea was this: after the haircut (provided you were good—no crying, no fidgeting), the hairdresser would take a lock of your hair and go behind a curtain, where the hair would magically transform into a toy, which would magically appear at the bottom of the curtain. The trick was nearly flawless and, save for the sharp disappointment brought on by the appearance of a human hand, I was enthralled.

Looking back, I’m not sure if the premise of the trick really included a transformation of hair-to-toy, but that’s the way I liked to think about it. Those were the days, after all, when lost teeth turned into quarters, and magic seemed an appropriate way to account for the private mysteries of the world.

I am reminded of the magic trick at Fantastic Sam’s every time I use a vending machine-- primarily because, in the years that have elapsed since early childhood, I have gained little insight into the workings of technology. I am no longer tempted to use magic to make sense of things, which is perhaps why I have largely stopped trying to make sense of things at all.

But science has a way of calling back our curious natures, however repressed by the constraints of experience. And so, recently, when someone asked how the MetroCard vending machines worked, I set out to find the answer…

We can account for most of the details using EVERY OTHER post I’ve written this week about MetroCards: the cards in the machine come encoded with certain information (serial number, expiration date), and a magnetic read head inside of the vending machine writes the rest of the information to the card when you buy it. If you pay by credit card, the same technology is at work: a magnetic read head reads your card, communicates with your bank electronically, and debits your account for the amount paid. The question that’s left to us, then, is how the machine reads cash and coins.

There are several ways that machines test the validity of cash. First, bills are printed with magnetic ink, and different bills generate different magnetic fields (magnetic read heads again, my friends!). Second, denominations have different fluorescent properties that can be detected using an ultraviolet scanner. Third, each bill is slightly electrically conductive, and its conductivity can be used to identify it. Fourth, and finally, digital cameras can measure the different optical qualities of a bill to determine whether it is counterfeit.

Although there are some fancy ways to read coins, most change is judged based on its physical characteristics alone: diameter, thickness, and the ridges that run along the edge. While this might seem like a security measure just waiting for a bored scam artist, the physical properties are difficult to replicate, and machines are picky—they measure each coin to the thousandth of an inch.

And how does your MetroCard get physically pushed out to you while you stand in front of the machine? Well, for starters, there’s a hairdresser…

*While these are true stories, I think it’s only fair to mention that my mother has given me plenty of good haircuts over the years. In fact, most of the time I got a professional cut, I’d come home and beg her to alter it. Most notably, I came home from Bumble and Bumble a few years ago looking like a Republican, and my mom fixed it. Thanks again, Mom.



The photo at right was taken during the Ann Arbor days. The haircut was courtesy of my older brother Gabe, who I mistakenly and unfortunately believed had my best interest at heart.