A method of ensuring that meat has been adequately cooked to doneness, wherein a substrate, such as a foil, film, fabric, laminate, label, card, or paper, having a thermo-sensitive color-forming coating thereon, is placed onto meat pieces such that cooking causes the coating to change color at a predetermined temperate. The working chest includes a casing, a upper lid, a nozzle holding dock, a nozzle, an air discharge filter device, an actuation switch, a left glove operation means and a right glove operation means. A first identity is determined for a first participant with a first confidence level. A status of a second switching element is controlled by the input signal and opposite to the status of the first switching elements A second current source is coupled to the second switching element through a second connecting node.