Estimating (Part 2)

The following points help us to have a better estimate for the system:

1. Understand what’s being asked - First part of any estimation is understanding what is being asked. Before giving an estimate, think about the scope of the domain. This is an important part in estimating. Often, the scope will form a part of your estimate: "Assuming there are no traffic accidents and there's gas in the car, I should be there in 20 minutes."
2. Build a model of the system - From our understanding of the system, we should first build a model of the system. This leads to discoveries of underlying patterns and processes that weren't apparent on the surface. For a project, the model could be the steps that our organization uses during development
3. Break the model into components - After building a model, the next step is to break our model into different components. We'll find that each component will typically have parameters that affect how it contributes to the overall model. At this stage, simply identify each parameter.
4. Give each parameter a value - After breaking the model into components, give each parameter a value. This helps to figure out which parameters have the most impact on the result, and concentrate on getting them about right.
5. Calculate the answers - Now, find answers by considering each component, rather than doing the estimation for that system as a whole. This helps to have better and more accurate estimation.
6. Keep Track of Your Estimating Prowess - It is always a good idea to record our estimates and sub-estimates. Sometimes, we’ll find our estimates are good. But sometimes, it may go wrong. When it goes wrong, instead of simply avoiding it, take some time to identify what went wrong. This will help to avoid the same problem from happening again. 

- summary of Estimating, from The Pragmatic Programmer: From Journeyman to Master