# Size versus Duration

Scrum introduces the concept of Story Points which most teams immediately misunderstand or discard. The most elegant wrong explanation I’ve heard for not using story points was:

“we never liked story points, because then we had to communicate and teach our customers a whole new currency.”

Fortunately, this isn’t true. *Un*forunately, the reason many find story points hard to implement is because we seem to have a hard time differentiating Size from Duration. Add *Effort* to the equation and you have your own little math game. In fact, you get the mathematics of Project Management. Blasphemy!

Here is the anecdote I’ve been using for a while now and it seems to work at least in explaining the difference. I have two puzzles, one with 25 pieces and one with 100 pieces. Each puzzle has pieces roughly the same size and complexity in imagery. That being said, the 100 piece puzzle is 4 times as difficult as the 25 piece puzzle. If I put 1 hours worth of effort into each puzzle per week, the duration until completion of the large 100 piece puzzle should be approximately 4 times longer. Ho long (duration) it takes me to complete the puzzle is a factor of the effort and size. Size doesn’t change, effort can.

Story Points are a * relative* unit of measure for size. If my only two tasks are the two puzzles, the smaller could well be 1 Story Point, while the larger would be 4 Story Points. If we find that a third puzzle of 12 pieces is added to the task list, it could be 1 Story Point, the 25 piece puzzle becomes a 2 and the final 100 piece puzzle would become an 8 Story Point Task.