Agile estimation is simple, because efforts are not estimated. Whoever learns from me, how to estimate Stories and Functionalities will quickly notice that I never estimate efforts, because that does not work. It is impossible because there are too many variables.
A training participant told me an anecdote: A hiker meets an old man in the mountains. He asks the old man how much time he needs to reach the cabin. The old man does not answer him, but instead uses his hiking stick to indicate to the man to just keep hiking. So the hiker continues on a little bewildered. From afar the hiker hears the old man call out: “three hours at that speed.”
This story explains what one must know: the speed of the hiker. Or in our case the velocity of the Team. Speed is a derived length of the distance divided by the time. If I want to estimate the velocity, I need to know the time.
The derived size may not contain temporal dimension, otherwise I would calculate the acceleration of the team. (Speed divided by time is the acceleration) . We must determine that we can indeed express a variable, that can define the size. The idea of the XP Community at the beginning of this decade was to determine the size of the stories: with help from Story Points.
So far so good. I have to measure the Stories, or estimate their dimensions in a unit that has no time frame. When estimating size don’t try to estimate the effort of developing the functionality, that already includes time in the concept of effort (effort is performance multiplied by time.)
That succeeds if you have a reference: take a story and simply try to define the “dimensions” of this story, which have nothing to do with the implementation of this story. Then you can use this story as a reference, give it a value and determine the development of all other stories based on this story. Voilà, with that all the stories have been estimated in their size.
Is that clear? Questions: If you do not want to believe what I explained above, open your Physic’s book and check out what it has to say about how to define size.