Making estimates on crop yield has been a farming practice for many centuries. Even today, experienced farmers are able to make rough estimates of the final crop yield, just by looking at the plant vigour and health status half-way through the season and taking into account the climatic conditions up until that point. Of course, estimates that are made nearer to the harvest season tend to be more accurate, as there is more information about how the crops progressed through the season, and also there is less time for things to go wrong.