"All the sheet metal knows is PSI at the contact patch" - that makes sense, Kerry; and I've been reading this thread from a couple of years ago:
http://allmetalshaping.com/showthread.php?t=10337
Thanks for the invite, also.
This is too advanced a topic for a newbie like myself anyway. The best way I'll learn the background of what everyone is discussing is practicing. There's an English wheel at an auto skill center I have access to a couple days a week, and the "adjusting dial"/jackscrew/turning wheel thing is on the bottom.
Peter, I am sure there is a huge joke in your statement that I'll learn about soon. For now, I haven't even learned the machine's nomenclature... All I know is it's a lot quieter (& easier) than me hammering!