There are 409 escalators on the London Underground. At present about 95 per cent of them are operational at any one time. Statistics come with a whiff of smoke and a flash of mirrors. Numbers are a distraction when the grind of a necessary escalator is silenced. They do, however, tell you that one dead escalator in twenty is more of a nuisance than you would have guessed, and they put what is demanded of public-service escalators into focus.