It's the best of its type.
Japan numbers = spot on. Famitsu/Media Create being close makes sure of that. Within 5%.
America numbers = very close. Within 10% usually.
Others = Not very precise. I'm guessing within 15%.
Those are weekly btw. For LTD, Nintendo, Sony and Microsoft keep on proving us close. But that's a bit because ioi isn't to proud to change the numbers. Therefore, I believe LTD numbers might be more precise on VGC than on NPD.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS







