Early in my teaching career, a student named Jon told me about an exciting investment. All through high school, he had been collecting plate blocks of postage stamps. At the time, postage stamps were printed fifty stamps to a sheet and the four stamps in a two-by-two block next to the sheet's serial number were called a plate block.
Plate blocks were rare because no one had ever thought to save them. Why would anyone want the two-by-two square of stamps next to the serial number? How often does anyone use four stamps to mail a letter?
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