How do you know when your turkey is done? For many Americans, the answer is when the little temperature gauge pops. Above is a patent for one such device, the "temperature signaling device," awarded to George G. Kliewer of Fresno, California, in 1970. As the patent explains the invention, "A food temperature indicator having a spring loaded indicating rod member releasable from a retracted position responsive to the disengagement thereof by a retaining member. ... To effect disengagement, the retaining member must displace a volume of fusible material." That's patent-speak for the material at point 46 becomes molten, the pin falls, and the indicator pops. Let's hope yours works as well as Kliewer imagined.
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