I have several different pieces of scrap fabric that I write the size of the needle on. I then attach the needle to it. I always know which size needle is in my machine - just look to see which of my scraps of fabric does not have a needle in it. I also write the date I start using that needle on the fabric as well. When I've written too much on my scrap, I then use it as a starter or ender when I sew.