The repetition code encodes 1 logical qubit in n physical qubits (|0⟩→|000…⟩, |1⟩→|111…⟩). Majority-vote decoding corrects any ⌊(n-1)/2⌋ errors. The threshold is p_th = 0.5 — below threshold, logical error rate p_L → 0 as n → ∞; above threshold it grows. The threshold is the crossing point of all curves.