Planning Poker® Cards, Mountain Goat Software. Used with permission.
... you have Product Backlog Items on your Product Backlog, and you need a system for estimating their effort in a robust way.
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It is important to have up-to date estimates. However, if you spend a lot of effort estimating in days or hours, and your velocity changes, then the estimates are all wrong.
The Product Owner needs to estimate a release date when a set of features will be done. Estimation points delivered per unit of calendar time yields velocity of feature point delivery. Hours delivered per unit of calendar time is a very poor measure of velocity and will confuse the product owner and cause dates to slip.
The Team needs to measure the impact of process improvement. Removing impediments will cause velocity to increase. Without a velocity measure based on estimation points, it is difficult and often impossible to assess the impact of a process improvement.
Therefore: Use unit-less numbers for effort estimation. Use relative estimation, based on a widely-understood and simple work item whose Estimation Points can be used as a baseline for the rest.
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Poker-planning is a modern implementation of the Delphi technique that has proven to be an excellent approach to generate estimation points. Poker planning is based on a nonlinear scale (approximately the Fibonacci numbers) that helps break down linear thinking.
Author: Jim Coplien