| http://www.w3.org/ns/prov#value | - For example U.S. Pat. No. 4,382,700 to Youngren describes an indicator which in a preferred embodiment includes a material such as mineral jelly, which is in contact with a wick, such as a wedged paper strip, such that the mineral jelly diffuses into the paper in accordance with changes in ambient temperature over a period of rime.
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