How to Knit a New Heel into a Worn Sock or Stocking

From Weldon’s Ladies’ Journal, January 1918.

How to Knit a New Heel into a Worn Sock or Stocking.

First procure wool to match the sock in colour and texture, and choose four steel needles which will give a similar tension in knitting.

Unravel the worn heel, being careful not to unpick a single stitch of the leg below the instep level.  Pick up on two knitting needles the stitches across sole of foot from one side of instep to the other to prevent them dropping. Now pick up stitches for the heel flap on one needle.  Join in the wool and knit to the last stitch on the heel needle, and slip one stitch of the side needle on to heel needle, and take these two together. 

Turn and purl to last stitch of heel needle, and as before slip one off from the side needle and take two together.  Do this at end of each row until the heel flap is long enough.  Count the stitches left at the centre of the sole of the sock, put them on one needle, then turn the heel by the same method used in the original knitting.  There should then be left on the heel needle as many stitches as were counted at the sole.  Hold the two needles together and take a wool needle and graft the heel and foot together.  All ends of wool, both old and new, must be darned in very neatly and securely, especially near the instep portions, and at the end of the grafting.

[I'm not an expert sock knitter, so this makes no sense to me.  It does imply that there was one standard way of knitting heels at the time, so if you had knitted lots of socks in that way, you might be able to follow the instructions.]