· 4 min read · Retival
Why a forecast should be a range, never a date
A single date pretends to know more than anyone does. A range says what is known, and narrows as the delivery is measured.
A forecast in Retival is a range of finish dates: an earliest, a likely and a latest. Never a single line, and never a probability. The range narrows as delivery is measured. A vague delivery gives a wide band, which is the correct answer.
One worked example
A milestone is wanted at week 12, with 1,200 productive hours of committed work. Before the buyer is invited, the range at day zero reads 10.91, 12.63 and 15.00 weeks. Week 12 reads: achievable, but needs better than this team's own average. Promising week 10 would warn both parties.
At week 5 the range reads 12.10, 13.20 and 14.72 weeks. The earliest possible finish has passed week 12, so the milestone reads MISSED, and the people with the mandate are warned before the deadline, not at it.
“When the revision arrives, it lands inside a band you have already seen.”
A state is a word
Each milestone is read against the range in four states: Ahead; On track, with downside risk; Achievable, but needs better than this team's own average; and MISSED. The product shows each with its word and a shape, never a colour alone.
A forecast is a claim, so it is graded
Every closed delivery tests the forecast that came before it: the week from which the range held the actual finish, how long before the finish that was, and how wide the range was then. The lead and the width always appear together, and a delivery whose range never held is shown as such, never dropped.