Methods of monitoring

Initial Post
The Project Manager’s success or failure will be determined, ultimately, by the bottom-line.

For this week’s discussion, comment on the following:

What are the tools and ways that project managers monitor and control projects? What are good methods of monitoring? How important is it to monitor the costs of a project? When should a project manager intervene?

For Example:
Cost variation analysis is one way a Project Manager manages by exception. If a project task is projected to cost $1000.00 but the actual cost was $1002.00, should a Project Manager be concerned? $998.00? $1100.00? $775.00?