T20 = treble 20 (60), D16 = double 16 (32), Bull = the bullseye (50), 25 = the outer bull. A checkout must finish on a double or the bull. A handful of numbers — 159, 162, 163, 165, 166, 168, 169 — cannot be finished in three darts; they are the “bogey” numbers every player avoids leaving.