PS4 sells 4.2 million WW as of Dec. 28th
PS4 sells 5.3 million WW as of Feb. 8th
PS4 sells 6 million WW as of March 2nd
January 2014 NPD - PS4 sells ~271K
February 2014 NPD - PS4 sells ~ 269K
Adjusting for 4 weeks instead of 5, we get approximately 880K untis sold WW between Dec. 28th and Feb. 8th, with ~271K units sold in the US in that timeframe, the US only accounted for approximately 31% of WW sales during that period
Between Feb. 8th and March 2nd, approximately 700K units were sold WW with approximately 202K units sold in the US [adjusted to 3 weeks instead of 4] which again puts the US at approximately 29% of WW PS4 sales
For the holiday season of 2013, PS4 sold 1138K [Nov.] + 865K [Dec.] which is 2003K out of 4200K WW at that time. Thus for the period of launch on Nov. 15 to Dec. 28th PS4 sold approximately 48% of its WW sales in the US
Using US LTD versus WW LTD as of March 2nd, we have 2543K out of 6000K which shows that 42.4% of PS4 sales are in US.
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Using the highest US ratio [48%], if PS4 sells 400K in the US in March we can expect 833K sales WW in the same time frame. It should be noted that this wouldn't account for Japan demand/sales or any other region added since Dec. 28th
Using the lowest US ratio [29%] we get 1379K sales WW for the March time period.
Using the US LTD versus WW LTD ratio [42.4%], we get 943K sold WW in that time frame although this would heavily favor the holiday months due to the unit sales
Using an average of the 3 separate time periods [36% = (29%+31%+48%)/3] US ratio we get 1111K PS4's sold WW in that time period
If PS4 sells 400K+ on March NPD I will be shocked if they don't reach 7M WW in that timeframe