The SSS Bow Clicker is a very effective tool that gives an audible click when you are at full draw, so you draw to the same length every time, thus giving consistent shots, improving accuracy.
To install peel off the paper to expose self self-adhesive, stick it to the limb, thread the cord through the bowstring  to the point where it clicks when you are at full draw, and knot the cord there or burn the end to form a button to stop the cord pulling back through the string & you're done.