1. On the Tools menu, click Options, and then click the Calculation tab.
2. Under Calculation options for Microsoft Office Project, click Manual.
3. To perform all calculations in all open projects, click All open projects, and then click Calculate Now.

   To perform all calculations in the current project, click Active project, and then click Calculate Now.

Note  By default, Microsoft Office Project 2003 performs calculations automatically. However, if you have a very large project, you may want to specify that Project perform most calculations only when you click Calculate Now, as automatic calculations can take a long time.