The main problem with the typical estimate is that it is a scalar number. 2 hours or five days or three months. That's fine if you are looking for a target to a

The main problem with the typical estimate is that it is a scalar number. 2 hours or five days or three months. That's fine if you are looking for a target to aim for. But if you want to actually know when something will be done and how much it will cost, a probability distribution with a confidence interval is the only reasonable way to model that.