Excellent instructions Rae.My method of culling chicks goes like this.
Your tools are a paper towel, a plastic sandwich bag and a heavy duty pair of kitchen sheers (scissors). You take the chick, and roll it up snuggly in the paper towel, making sure you can feel where the chick's neck is through the paper towel. This calms the chick and makes the next part easier. You place the chick/paper towel roll half in the sandwich baggy leaving the head and neck out. Take the scissors and swifty snip through the chicks neck through the paper towel. You don't want flimsy paper scissors, because they an bend and not do the job effectively. It will take a few seconds but you will start to see blood on the paper towel. When you finish the cut, before you start seeing blood, you can push the paper towel all the way into the baggy to contain any mess. If you like you can seal the bag and toss it like that, or take it out to the compost pile, dig a hole and bury the chick in the paper towel.