Cumulative temperature is expressed in degree-hours or degree-days. For each day, degree-hours are determined as the product of the length of time, in hours, during which temperatures are above the standard, and the amount, in degrees, by which the mean temperature of the period exceeds the standard. Division of the resulting degree-hour value by 24 gives a value in degree-days. Summation of either over the period of interest creates the accumulated temperature.