In other words, a constant amount of thermal energy is required for the growth and development of many organisms, but the time period over which that thermal energy is accumulated can vary. Many organisms slow or stop their growth and development when temperatures are above or below threshold levels. The accumulation of thermal energy over time is known as degree-days or heat units. Degree-days and other heat unit measurements have been used for determination of planting dates, prediction of harvest dates, and selection of appropriate crop varieties.

Adcon's Heat Unit extension, which is part of our data visualization and distribution software addVANTAGE Pro 5.4, includes the most commonly used methods for calculating heat units. The user is able to create templates based on information found in published models. The templates can include the method of heat unit calculation and thresholds levels for alarms - crucial for precise management decisions.

Chilling Units
Chilling units values are used to predict several management factors. Fruit growers are the primary users of chilling hours. Decisions such as varietal selection, pruning, and other management factors related to potential yields can be aided by chilling hour calculations.

Calculation Methods
Eleven calculation methods are provided in Adcon's Heat Unit extension. Each degree-day calculation method estimates the area under the daily temperature curve above the lower developmental threshold. The calculation methods available in Adcon's Heat Unit extension include: Averaging, Standard, GDD (Growing Degree-Days), Single Triangle, Double Triangle, Single Sine, Double Sine and Near Real-Time.

Cutoff Method
The cutoff method is also a key component of a phenological model and is typically indicated in published phenology models. The cutoff method modifies the daily degree-day calculation to more accurately reflect an organism's growth response to high temperatures. Three cutoff methods are included in this extension. They are the Horizontal, Intermediate, and Vertical cutoff methods.

User Friendly Model Template
Adcon's Heat Unit extension software includes a template that makes creating customized phenological models very easy. Simply select the calculation and cutoff methods from the pull-down menus then enter the threshold values and alarm values into the appropriate boxes. The new model can then be saved for future use.