Abstract
Inaccessible area (IA) is the set of pairs (D,E), D and E are project duration and effort, that cannot appear. IA is related to the changes of effort consumption dynamics (ECD) for tight project durations D.
The widely used Rayleigh model RM of ECD does not imply the existence of IA and the behavior of project efforts for projects having (D,E) near their IA's. Let $t_{max}$ be the time when effort intensity E(t) is maximal.
RM requires that the effort E expended before $t_{max}$ is near to 0.52 E. RM implies almost no effort consumption for $t } 3.5 t_{max}$.
It wrongly implies that zero defect software could be a feasible goal. We propose a new model M inspired by physics having no such drawbacks.
M can be used to refine estimations of D and E after $t_{max}$ is passed. The model implies several mutual dependencies of empirical laws of software development.
M implies the behavior of effort E near inaccessibility area and implies a realistic estimation of project duration.