Telltales, those bits of flying wool or sail cloth that indicate what the wind is doing. But what do they tell you.
Reading Telltales is quite easy so lets go for the simple mans guide
TellTale points upward: Wind has stalled over the Telltale… i.e. instead of flowing past the teltale in nice smooth flow its breaking up and creating eddies. you want the Telltales all flying straight back when going up wind. If its the outside telltales (leeward) ease the Genoa sheet, if its the inside (Windward) tighten the sheet.
TellTale points downward: Wind is being pressed against the sail instead of flowing across it. You will see this when going downwind and its a good thing, but upwind you want to move the sail until you get smooth flow again. If it’s the Leeward ones pointing up, tighten up on the sheet, if its the windward, loosen up on the sheet.
Its that easy. Of course it gets more complicated, like setting up the traveller and Genoa blocks but start with getting them mostly flying smoothly across the sail (Genoa we are talking about) and if you can’t get them doing it for the entire height of the sail, you need to move your Genoa blocks to adjust the twist. Play until its right.