Comparison
Cone of uncertaintyvsEstimate
Cone of uncertainty
you were asked for a date before anyone had opened the vendor's documentation, and gave one.
The observation that estimates are wildest at the start of a project and narrow as work is done and unknowns are resolved. It is a reason to give ranges rather than points early, and to re-estimate as evidence arrives rather than defending the first number. The practical use in a conversation is to say where on the cone you are: an estimate made before a spike and one made after are different kinds of claim.
Full entry →Estimate
you said about three weeks, and heard it repeated in a meeting as the date it will be done.
A probabilistic statement about how long something is likely to take, given what is known now. It is not a promise, and the entire dysfunction of software planning comes from the two being conflated somewhere between the engineer and the roadmap. Stating the confidence and the assumptions along with the number is what keeps it an estimate on its way up the organisation.
Full entry →