“Everything went as planned until Toptunov accidentally missed a key step in the operating procedure. All he did was forget to flick a single switch, but this was to have enormous consequences. The switch operated the automatic power-reduction controller, and by not activating it – while believing he had – Toptunov ensured that neither he nor the control centre’s ‘autopilot’ were regulating output levels inside the reactor. The result was a sudden and huge power drop, from around 520MW, about 18 per cent of the reactor’s usual output, to just 30MW – a negligible 1 per cent of the reactor’s full capacity.”