Exercise 3: A Fifth Phase — Code Review Complete — Possible Solution
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SETUP
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    'Code review complete': (0.97, 1.03)

RESULTS (all five phases)
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    Initial concept:          252 - 4000 (3748 hours wide)
    Requirements defined:     501 - 1999 (1499 hours wide)
    Design complete:          671 - 1498 (827 hours wide)
    Implementation underway:  900 - 1100 (200 hours wide)
    Code review complete:     970 - 1030 (60 hours wide)

    Narrowing factor, Initial concept -> Code review complete: 62.7x

WHY THIS WORKS AS AN ANSWER
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Extending the chapter's own progression by one more phase continues
the exact same pattern: the range keeps narrowing, from a 3,748-hour
spread down to just 60 hours - a 62.7x tighter range than the earliest
phase, well beyond the chapter's own reported 18.7x at "Implementation
underway." This makes the shape of the cone concrete at its narrow
end: by the time code review is complete, the true effort is
essentially known (a 60-hour range against a 1,000-hour true value is
a 6% margin), which makes intuitive sense - almost nothing about the
work remains undone or undiscovered at that point. The whole point of
the cone's own shape is that this narrowing isn't optional or
skill-dependent; it's a direct, structural consequence of how much of
the actual work has already been completed by the time the estimate
is made.