Bushel Farm uses the USDA's growth stage model for corn as a default, which is based on Growing Degree Days (GDD). This is an 86/50-bounded calculation, which only accumulates when temperatures are optimal for corn growth. This means that we take the average temperature of the day (bounded by a minimum of 50° and a maximum of 86°) and then subtract 50 to provide you the average number of degrees above 50° that the crop accumulated.
Additional GDD calculations such as GDD 60, 55, 45, and more are available when viewing heat units from all years from a field's detail page. Cumulative and daily heat units from all years are included in the Rain and Heat History feature.