Every Timestrip® PLUS product is calibrated to a temperature of 2ºC above its stated threshold temperature. For example, Timestrip® PLUS 12ºC is calibrated to a temperature of 14ºC. When the product breaches its threshold temperature and is held at a constant temperature(i.e. isotherm) of 14ºC, it will reach the 1 Hour print mark within 1 Hr (+/- 15% in time).