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Relative estimates are like a stagecoach

If you're having trouble getting across the idea of relative estimates (story points) vs velocity to your management, try this approach:

Estimate story size using a distance measure. Furlongs for fun, miles if you're a boring American, kilometers if you're a boring person on the rest of the planet.

Your team velocity is measured in furlongs-per-sprint. This makes clear the separation between the amount of work to be done vs the rate at which a team can complete it. It calls out the adjustments that management can make to the project: go faster, do less work.

The stagecoach itself represents overhead.  Every new horse added to a stagecoach adds to its potential speed. Four horses is better and faster than one horse, but not four times better. There's a point where you're better off with two stagecoaches.

Here's how it might play out at your company:

Feature A: 3 furlongs

Feature B: 8 furlongs

Feature C: 5 furlongs

Feature D: 8 furlongs

Your team of 5 people completes about 10 furlongs per sprint, with a sprint being 3 weeks long.  Business wants to be done with this in two sprints.  That gives you a capacity of 20 (10 furlongs per sprint * 2 sprints).  But you can see that the sum of the work is 24.  You need to either drive longer (do another sprint), stop sooner (choose a feature to cut, or make sacrifices in all features to cut 4 furlongs total), or get some more folks in this and the next sprint to do the work -- a 20% horsepower increase, which translates into one more person if they don't need to ramp up on anything.

That's a solid conversation with management, based on fact.  And you are the heroic Pony Express!