Imagine you are a hospital doctor. Some patients die. But how many is too many before you or your hospital are labelled killers? We've devised a chance calculator to simulate this scenario. It is set up so that you are innocent of any failing. But bad luck might convict you all the same. In the real world all kinds of factors make a difference, like surgical skill. But in the calculator, every patient in every hospital has exactly the same chance of dying and every surgeon is equally good. This is to show what chance alone can do, even when the odds are the same all round.