We and everybody relies on the NPD Group for retail sales here in North America. And by everybody I mean everybody. II've had Sony, Nintendo and Microsoft all tell me to wait for those numbers when I asked them how their consoles were doing.

But how does it work? I know, for instance, they can't track Wal-Mart numbers and I'm pretty sure they don't track the little guys either.

When the group sent out their latest numbers, this time for the PC in 2006, they included a brief explanation and I hit them up for a bit more details to walk you through the process.

According to the group they get sales date from about 60 percent of U.S. retailer. They don't, as I suspected, get any numbers from Wal-Mart. That's because the super store doesn't give anyone that information.

What NPD does, and this is really what they are all about, is make projections about what sales they think Wal-Mart and the remaining retailers did using "sophisticated projection methodology."

So a whopping 40 percent of gaming retailers don't provide any data. Yikes, that's like 10 percent away from a coin flip. Brian Crecente