Some patterns require you to make double-sided prints. Since most of us don't have printers that can handle "full duplex" printing, we have to print the first side of the pattern, stick the paper back into the printer upside down and print the second side.
Sounds simple? Believe it or not, I still make plenty of mistakes putting the paper back into the printer in the correct orientation. Here is the easiest way I have found to make a fool-proof double-sided print.