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July 25, 2003

Strange But True!

By BILL SONES and RICH SONES, Ph.D.
Special to the Journal

Q. How do dollar bill changers know when someone has slipped in a bogus buck?

A. One method uses magnetic heads like in a cassette tape recorder to read the magnetic ink signals coming off the bills, says HowStuffWorks.Com. Electrical conductivity is also telltale, as are the fluorescent properties of the ink and paper, or optical properties read by a photocell or camera. A good bill changer will use several of these.


 
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