Putnam–Norden–Rayleigh curve

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In the study of software project scheduling, the Putnam–Norden–Rayleigh curve, also known as the PNR curve, is an equation specifying the relationship between applied effort and delivery time for a software project. A PNR curve can be used to determine the least cost time for delivery up to the limit , the absolute minimal amount of time required to complete the project no matter how many human resources are added. The PNR curve was used to derive the Software equation.[1]


The following equation shows the relationship of project effort as a function of project delivery time.


  • =Effort in person months
  • =The nominal delivery time for the schedule
  • =Actual delivery time desired

See also[edit]


  1. ^ Pressman, Roger S. (2005) [1982]. Software Engineering – A Practitioner's Approach (6th ed.). Newyork, NY: McGraw-Hill. pp. 678–679. ISBN 0-07-285318-2.