If you did not know about this command you are really missing out. If you are in the scale command and have picked objects to scale and a base point, you can specify by reference by typing an R. I do this all the time when I don't know at what scale something drawn, but I do know a specific portion like a door is 3 feet. I click off the width of the door and type 36 to scale the entire drawing down to the nat's booty.
I just talked about about it. Check out Autodesks super tip on Scale reference.