I was looking at a burn-up chart spreadsheet recently, and (for some weird reason) started trying to add up the numbers by hand (iPhone calculator, actually). My suspicions were correct: Excel was adding incorrectly.
"InconCEIVable!" I shouted. Microsoft, make a mistake of this magnitude in an app? If Excel couldn't add, the entire US economy would probably collapse. (First sentence is sarcastic; but the 2nd is said with a straight face and a nervous twitch.)
Turns out, I wasn't viewing digits to the right of the decimal place. No matter what Alan Cooper might say about that, this was clearly my own "user error." (More sarcasm, by the way.)
The team had 1/2 point estimates on stories here and there, and that was throwing off my interpretation of Excel's display of the data.
I decided to ask the team why they were using 1/2 points. After all, story points are unit-less, so we could just multiply all estimates by two, and my brain would not have had to grok Excel's annoying user interface.
I wasn't asking them to change their estimation methods, or their existing estimates. It was instead a rhetorical question. Thankfully, they had grown used to my peculiar goal-less, blameless way of asking questions (which I stole from James Shore, the Walking Root-Cause Analysis Machine, by the way), and someone easily replied...
"Because the deck of Planning Poker(c) cards contains 1/2 point playing cards, so we used them."
My face twisted, turning bright red, and then it happened... "COHN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
:-) It's not really Mike Cohn's fault. Well, okay, maybe it is, but big deal. I'm not really upset with Mike; it just makes for good blog post fodder. In other words, I do think there's something odd about 1/2-point estimates, and maybe something we can learn here.
Disclaimer: Also, Mike is a friend of a good friend (Hi, Bob!), and I think I've even friended Mr. Cohn on facebook (Uh, when did "friend" become a verb, anyway?) He's also a very smart guy, and has loads of very good Agile books published, and has those slick Mountain Goat Software Planning Poker(c) cards. Please, Mike, don't take it personally.
One does not want to get on Cohn's naughty list: He'll chase you "round the Moons of Nibia, and round the Antares Maelstrom, and round perdition's flames..."
But please, let's throw out the 1/2-point cards.
I like to suggest this method as one way to start estimation: By thinking of the smallest, simplest--but whole--bit of deliverable software that you could imagine building, and giving that 1 story point. So a 1/2 pointer is a strangely broken story, using that algebra.
Another way of looking at it, a 1-pointer is something you could get done in a couple hours.
Now, yes, I just mentioned time (bad, bad, bad...), which has little to do with Story Points, but a 1 equaling approximately 2 hours does not imply that a 2 is approximately 4 hours. After all, the margin of error in the conversion increases as the scale increases, and ya gotta go to lunch sometime! A 2 is simply twice as complex as a 1.
Why do I care so? Because removing the 1/2 pointer simplifies the math. Sure, adding 1/2 points is easy. But not adding them up is easier, and the team could keep a running total in their heads while they plan, for example. Save your brain's electrical current for things that matter, like Star Trek trivia. Not Excel's ridiculous user interface...