If you have a D-Cup Spread 3/4"
If you have a DD-Cup Spread 1"
If you have an E-Cup Spread 1 1/4" (you might want to draw a double set of lines spaced 1/2" apart.
Slash and spread each 5/8" instead of trying to spread one line 1 1/4"
F-Cup Spread 1 1/2" definitely drawing two lines to work with (spreading each 3/4".)
--If anyone needs help with this, please let me know and I will draw it out for you--(anytime I offer, I mean it sincerely!)
If you have a bust size larger than that, I would plus-size the pattern first. (Check out the post I did in Oct, 2008 showing how to do that.)
My full bust measures almost 41" -- I cut out the size xl.
Then, slash the lower front pattern piece along the horizontal line. Anchor the top edge to the pattern paper with some tape and spread the lower half 3/4". Also, trim off the little triangular piece and spread that 3/4" from the center piece as shown.
Use a French Curve to "true up" the top curved edge of the lower front pattern piece. You will end up trimming off some of the existing pattern. True up the lower edge of the side front pattern piece as well.