I wonder why the PS3 sales are lowered when overtracked, yet when the 360 is overtracked and PS3 is undertracked everything stays the same.

I wouldnt mind an explanation when things like this happen. Just a
"according to sources we overtracked the PS3 the weed of ______" and the numbers were adjusted.

IS this from the holidays? This year? Its hard to argue the numbers and use them as reference when they change so often for reasons we don't know. I therefore always need to start off all my arguments with "as of now.." when referencing vgchartz.

@ssj12

yup, same here...

cus 360 is usually lower on NPD, Ps33 higher...

wii is sometimes low, high/on the dot

20 million not 10

I just would like to know what source is more credible than NPD? It would have to be something significant if NPD isnt credible enough yet this other source is. Oh well though, it still seems the PS3 will continue to close the gap weekly, yet it wont reach 10 mil before the 360 hits 17 mil anymore

Shipping numbers by the companies for one. From shipping numbers you can estimate remaining stock, and therfore sales more accurately then you can NPD. The problem is... you have to wait.

Then you have the fact that NPD does nothing with Europe or Japan.  And that NPD has been off recently vs said shipping numbers. 

Who by the way often offers corrections and retractions that the populace never sees. (I believe anyway)

Therefore if you add up every monthly released numbers they would almost certainly not equal NPD's actual end of year numbers.

 The reason for that is because of selective memory on your part.  The other numbers get adjusted all the time, you just don't pay as much attention to it.  When the 360 was hitting 10 mil, it got adjusted down several times and there were lots of people complaining about it.  They all get adjusted.

Oh and other source more credible than NPD is the Company reports.  While those numbers are shipped to retailers, they do give a general idea of where the numbers should be.  For example, the Wii was actually undertracked a little bit according to Nintendo's annual report. 

Every time ioi puts out new numbers he re-evaluates previous weeks based on new findings that way he is as "accurate" as possible to the factual information. Otherwise there is a good possibility that when quarterly reports and other such reports from the manufacturers are released the site stays within the margin of realism.

@Jandre: The difference is that VGC wants to use it's own data and NPD was in VGC:s neck a year ago for using NPD numbers.

10.5 million? Where comes this number from?