Video: Alternating Cable Cast-On
The Alternating Cable Cast-On is a very stretchy and almost invisible cast-on for any combination of knit and purl stitches.
As with the alternating long-tail cast-on, the "knit version" of the alternating cable cast-on is the regular cable cast-on you've learned, and the "purl version" is the opposite movement.
You can alternate 1 knit and 1 purl to prepare for 1x1 rib, or you can alternate 2 knits and 3 purls to prepare for 2x3 rib, etc.
1. To make the last cast-on stitch look just as good as the rest of them, bring your yarn between your needle tips to the other side of your work after creating the last stitch but before placing it on the left-hand needle.
2. Because you don't have to turn your work after doing this cast-on, take care to start with a purl stitch and end with a knit stitch so that when you start working into the cast-on, your first stitch will be a knit stitch, and you'll start the row off in the expected way of "knit 1, purl 1..."