The stretchy cast-on

Take a yarn of a different color than the one you are knitting. Cast on half the number of stitches you need plus one stitch.

Calculation example:
If you need to cast on 45 stitches, cast on with the yarn of a different color: (45+1) divided by 2 = 23 stitches.

With the yarn intended for knitting, work as follows:

1st ROW:
* 1 knit stitch, bring the yarn to the front of the knitting by passing it under the needle, 1 yarn over *.
Repeat from * to *. End with 1 knit stitch.

2nd ROW:
Take the first stitch as if to purl it and slip it onto the right needle without knitting it, * pass the yarn behind the knitting, knit 1 stitch (= yarn over from the previous row), pass the yarn in front, 1 slipped stitch purl *.
Repeat from * to *.

3rd ROW:
* 1 knit stitch, bring the yarn to the front, 1 slipped stitch to the back, pass the yarn to the back *.
Repeat from * to *. End with 1 knit stitch.
Continue in 1/1 ribbing, starting the first row with 1 purl stitch.
Remove the colored wire from the assembly