Abstract: A time temperature indicator in the physical form of a substantially planar label-like member that can be placed on perishable products to give a visual indication of deterioration or spoilage of the product due to its exposure to temperature. The indicator includes a galvanic cell which serves both as power source and, by virtue of a partly consumable electrode, as an indicating coulometer, indicating charge transfer wherein the charge transferred is an electrical analog of the time integral of the deterioration rate of the product as a function of temperature; the analog of the deterioration rate is the current drawn from the cell when a device having a current drain which is an approximate exponential function of temperature is connected to the terminals of the cell. The visual indication is provided by the contrast of the prearranged pattern of a protected part of the consumable electrode against the electrolyte which becomes visible when the unprotected part of the electrode is consumed.