I am using Jo's pattern, which she adapted from a pattern in Norah Waugh's Corsets and Crinolines. My friend Jana, who is a graphic designer, enlarged it for me so it was true to scale.
The background came out dark, so I decided to retrace it using our glass door as a light table. Because I didn't read the step one instructions clearly, and thought I needed to add the extra measurements around the pattern pieces. It was only after I was done laboriously retracing the pattern onto white paper that I realized we are adding the extra measurements into the middle of each pattern piece. Oh well.
Step 1: Subtract 2-3 inches from your waist measurement. I took away 3 inches. I had to enlarge the pattern to accomodate my waist, so I then subtracted the pattern's waist measurement from mine. Divide the difference by five because you will have to enlarge the five pattern pieces. In my case I have to add 5/8" to each piece.
Step 2: Number each pattern piece from left to right.
Now to add the extra inches to the pattern pieces... Draw a line up the center of each pattern piece using a ruler. Cut (the "slash" part of the process) along the line.
Step 3: Tape a piece of paper underneath the left half of the pattern piece. Measure and mark 5/8" from the cut edge in several spots from the bottom to the top of the pattern piece.
Step 4: Attach the right half of the pattern piece along the marks you've made. I found it easiest to tape it at the top mark, then align it at the bottom mark, double-check that the space measured 5/8" at both top and bottom, and then tape it in a few places along the pattern piece to secure it.
Make sure the lines on the waist match between both pieces!
Step 5: Do Steps 2-4 for each pattern piece. It was a lot easier than I thought it would be! Maybe partly because I retraced each piece, which ended up being a really good study of how each piece is constructed (with boning channels drawn in, etc.).
Each piece has been slashed, spread, and reassembled with 5/8" added to each piece.