Clean Coder, The: A Code of Conduct for Professional Programmers (Robert C. Martin Series)

by Robert C. Martin

When you estimate a task, you provide three numbers. This is called trivariate analysis: • O: Optimistic Estimate. This number is wildly optimistic. You could only get the task done this quickly if absolutely everything went right. Indeed, in order for the math to work this number should have much less than a 1% chance of occurrence.2 In Peter’s case, this would be 1 day, as shown in Figure 10-1. • N: Nominal Estimate. This is the estimate with the greatest chance of success. If you were to draw a bar chart, it would be the highest bar, as shown in Figure 10-1. It is 3 days. • P: Pessimistic Estimate. Once again this is wildly pessimistic. It should include everything except hurricanes, nuclear war, stray black holes, and other catastrophes. Again, the math only works if this number has much less than a 1% chance of success. In Peter’s case this number is off the chart on the right. So 12 days.