You'd like to estimate your project's cost or schedule accurately. So far, none of your approaches have worked. It's time to consider how you can create an accurate estimate.You might not be able to develop an estimate at the beginning of a project that is good until the end. Few project teams can. Instead, learn a number of ways to see your project and how to address your uncertainties in ways your managers will accept. Это и многое другое вы найдете в книге Predicting the Unpredictable. Pragmatic Approaches to Estimating Cost or Schedule (Johanna Rothman)