All processes have variation, no matter how undesirable it is. For example, the earth takes about 365.25 days to revolve around the sun. What most people don’t know is that that figure is just an average: sometimes it’s a bit more and sometimes it’s a bit less. Variations in production, however, inevitably cause waste. The key to Lean processing is identifying the cause of variations and resolving them where possible. Variations usually arise from three key areas.