A tell-tale is a piece of yarn or fabric attached to sails or rigging on sailboats, used to guide sail trimming by indicating airflow and proper sail position. Tell-tales come in three types—draft, leech, and shroud—and help sailors adjust sails by streaming aft when properly trimmed or spiraling when airflow detaches. A tell-tale compass is also a cabin-mounted navigational instrument that allows captains to monitor course from below deck.