Knitters' delight: perfect tubular ribbing cast-on

For a change, I share this technique learned two-thirds of a lifetime ago. Credit to Heather Halcrow Nicholson

1. Using any contrast yarn and speedy method, cast on HALF the number of desired stitches.

2. Knit one row in contrast.

3. In proper project yarn, knit 5 rows Stocking Stitch, beginning and ending with knit rows.

Now for the cool bit. 

4. P1 from the needle, move the yarn to the back.

5. With the left needle, pick up the bottom-most loop of project yarn where it pokes down below the contrast.

6. Knit this stitch. Move yarn to the front.

Repeat steps 4-6, alternating purling from the needle with knitting from the bottom row of project yarn loops, until all stitches have been purled from the needle. 

Voila! The knit stitches have created the tube and you have the correct number of stitches. Continue in k1, p1 rib as required. Unpick/snip out the contrast yarn whenever you like.