A timing device for visually indicating the passage of a duration of time is disclosed. The timing device and system, in accordance with the embodiments of the invention, is sectioned into zones with different rates of reactivity and/or sensitivity, such that the zones change color or darken over a range...http://www.google.ca/patents/US6822931?utm_source=gb-gplus-sharePatent US6822931 - Timing system and device and method for making the same
