Dr. CASTRO: Then if it's positive, you add another couple of weeks for drug resistance testing, so you can see already a month interval easily going by before you have any result where you can hang your hat on.

NPR: TB Traveler Exposes Diagnosis Problems

By reading the encrypted data off of two cards and testing thousands of potential site codes against both cards until the decoded data displays a predictable interval between the two, he can find the site code and use it to create more card keys with a magnetizing device.

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