Question About Double Die And MD

Here is a thread that I posted on a while back that the subject was discussed.
http://goccf.com/t/300641
Raised devices are what we often see on coins. The die design is incuse or negative of the coincidence design. They are mirrored so they will be a positive on the coins that are struck.
Incuse devices are sunk into the coin. Previous examples have been the VDB on the shoulder of the Lincoln Cent. The shield cents have the EPU design as incuse now. The ATB parks quarters have letters on the reverse ring, that are incuse. I took 100 of them and determined that 70%of them had some Machine Doubling on them. A number a lot larger than I expected. But to make the services on coins, the devices on the die need to be raised and mirrored. The slightest die movement before or after the strike will alter the devices. Hope this helps.

http://errorvariety.com/
John1

dbrablec, quite right, but in today's idiotic frenzy of megabuck hopefuls, even logical minded experts seem to have gone off the rails. That line of formal definition has been lost, what was once the easy distinction between a "mint production" error and a "mint striking" error is blurred.

So what would be considered an error? So double dies aren't errors they are varieties... and if course md is simply mechanical error not human error as with a dd variety....im thinking that errors would b something like a mule or wrong date or mint marks and such