26 November 2012:
I have just uploaded an expanded version as a full sock pattern (dither2.pdf). I am leaving the original live for the moment, as it is still very easily adaptable for other garments.
You should have knit stranded socks before, as this will give you an idea of how many stitches you will need to cast on and how many rows you will need for the foot.
If you have any problems adapting the chart please feel free to send me a message.