Fish freezes at about -1°C, therefore in the measured freezing time the effective temperature difference is 34 degC (the difference between -35°C and - 1°C). The effective temperature difference for the freezing time required is 24 degC( the difference between -25°C and -1°C). Freezing time is inversely proportional to the temperature difference, therefore the freezing time with an operating temperature of -25°C will be longer than for a temperature of -35°C and can be calculated as follows: