Intarsia patterns require the knitter to switch out different colors (balls) of yarn for stitches without carrying the second strand of yarn behind the knitting. The most common way intarsia is used is in argyle socks.
You can imagine that with all the colors being switched around that there are a lot of yarn ends to be woven into the back of the knitted piece. The best way to do the weaving is to use the duplicate stitch. If the weaving is done carefully you can't even see where the ends are woven in.
Needless to say, I'm really excited! I have been working on this program for nearly eight years. It's true that I have lost my father, moved three times, married off three children, and gained a grandson during the eight years, so some years I haven't worked all that hard on it. It feels so very good to have finally finished what I started.