Then the model planet starts spinning and goes into orbit around the sun. The computer then begins to crunch the numbers. It divides the Earth's surface into 16,200 squares and keeps track of approximately 75 variables for each square. It divides the atmosphere into 18 layers, giving itself almost 22 million points to calculate. It calculates and records these points every 30 minutes on the model Earth.
Earth takes one day.
As the model planet spins, the computer tracks variables such as average annual temperature until the Earth has calmed down from the initial shock of unusual conditions Sloan supplied it with. It typically takes 12 model years for variables such as average annual temperatures to stop fluctuating in the computer model Sloan uses. Then Sloan lets it spin for a few more years. She analyzes the climate variables the computer produces for those years only. The entire process takes about 300 computer hours on a Cray supercomputer.