Detailed estimates are sometimes referred to as bottom-up estimates, because they are based on all the various steps involved in project planning. A detailed estimate includes all the schedule and resource information (as discussed in Chapter 7) and a forecast of a project budget and cash flow (described later in this chapter). This is the estimate that will be used to manage the project and evaluate its success.
There is a huge difference in accuracy between an order-of-magnitude estimate and a detailed estimate, because the latter assumes a detailed understanding of the product and is based on the availability of key resources. Enormous amounts of work specifying product requirements and design work take place between the order-of-magnitude estimate, when there are no specifications, and the detailed estimate, which is based on specifications. This work required large expenditures of time and money, but this money was not spent until the inexpensive ballpark and the order-of-magnitude estimates had determined that the project was feasible.
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We can all recall situations where we have utterly failed to listen to what someone else is saying. For various reasons, we are simply not taking in anything useful. How many times have you been introduced to a person by name only to not know what their name is thirty seconds later?