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From that contract that was linked elsewhere, the equipment being provided includes:

> One (1) VX680 GPRS Terminal w/battery, thermal printer

The VX680 is a mobile credit card terminal (http://www.verifone.com/media/413350/VX680_2_lg.jpg) made by Verifone, much like the type that restaurants use most places besides the USA. If I had to speculate, maybe they try putting varying charges/holds on the card and see when it gets rejected in order to divine the balance?

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