An array of thermochromic cells is formed along the end portion of a thin, highly conductive blade. Each cell is visually responsive to a critical temperature incrementally different from the critical temperatures of the other cells. The thermochromic array defines a set of temperature ranges, set off...http://www.google.com/patents/US4445787?utm_source=gb-gplus-sharePatent US4445787 - Surface temperature measuring device with reversible thermochromic film
