In the United States, NPD December accounts for nearly 25%, while October, November, and December account for 50% of the calendar year's revenue. Additionally, history shows that from January to October within any given year the data for a system's installed base is roughly a linear function. This is always subject to change if there is a price cut or a system seller game like Halo.[1] In addition, November's hardware numbers are often 2.5 times greater than October due to holiday's gift-giving nature.[2]