How to Use A Lifeline
A lifeline is ideal if you are making a pattern that is large and/or complicated for you. It is often used in lace knitting, but can be used in any type of knitting and by knitters of every skill level. By threading a string through your row or round of knitting where you know you are correct, you can later frog (undo) your knitting if you make a mistake. You’ll be able to put the stitches back on your needle without dropping any or getting them twisted. When doing a difficult lace pattern, it is a good idea to place a lifeline about every 10 rows, so if a mistake is made you won’t have to frog too much of the work.
Placing the Lifeline
To make a lifeline, you will need a yarn needle (the same one you use to weave in your ends) and a smooth contrasting piece of yarn or string. Make sure your contrasting piece of yarn is not one that might rub color off onto your project, or one that is bulky or textured. Ideally it is smaller than the yarn you use for your project. Some people like to use plain dental floss. The yarn for the lifeline should be longer than your piece of work.
Knit until you are ready to put the lifeline in. Count your stitches and check the pattern to make sure you are happy with how the project looks so far.
Thread your yarn onto the yarn needle, and then thread the yarn needle through every stitch on the needle. When you've finished, you will have a piece of yarn and the needle through every live stitch.
Remove the yarn needle, and leave the lifeline in place. Ignore the lifeline, and continue knitting in pattern.
Using the Lifeline
Use the lifeline when you find a mistake in your pattern and you need to rip out rows to remove it.
Remove the needles from your project, and frog (rip out) the project until you reach the lifeline. Once you reach the lifeline, your project will not rip out any more until you remove the lifeline, so you don't have to worry about accidentally ripping back too far or about dropping individual stitches.
Now, place the stitches on the lifeline back onto the needles, making sure not to twist them, and start knitting again.