You take a piece of string and tie it 1-2 feet above the main top block on the wire of the back stay and wrap rigging tape around the wire just below it a bunch of times so it does not slip down the wire. Then you run the string through the stern cleats on either side up to the traveler cleats on either side. Tie the string to those horseshoe shaped pieces of metal on top of the traveler cam cleats. Now when you do this make sure that the backstay is at the light air setting as not to effect the tension of the backstay or the string. It should be snug. After tacking the helmsman eases out the main sheet out a foot (in the sheet or traveler) and yanks the windward string at the same time. This whips the backstay to windward as the main drops to leeward. This keeps the crew from jumping on the stern and allows the helmsman to be minimally distracted.