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delay at this point has unusually severe financial, as well as psychological, repercussions. The project is fully staffed, and cost-per-day is maximum. More seriously, the software is to support other business effort (shipping of computers, operation of new facilities, etc.) and the secondary costs of delaying these are very high, for it is almost time for software shipment. Indeed, these secondary costs may far outweigh all others. It is therefore very important to allow enough system test time in the original schedule.

When a task cannot be partitioned because of sequential constraints, the application of more effort has no effect on the schedule (Fig. 2.2). The bearing of a child takes nine months, no matter how many women are assigned.

For some years I have been successfully using the following rule of thumb for scheduling a software task: 1/3 planning 1/6 coding 1/4 component test and early system test 1/4 system test, all components in hand.

Oversimplifying outrageously, we state Brooks's Law: Adding manpower to a late software project makes it later.