Comment by twic
That concept of velocity is in the original Extreme Programming practice, which predates Pivotal, and it was indeed done with racks of index cards.
It's explained pretty clearly in the first edition of Extreme Programming Explained, but i can't find a copy of that online right now. The second edition was absolutely ruined for some reason, but still contains a rough description of it:
> Whichever units you use, hours or points, you will need to deal with the situation where actual results don't match the plan. [...] If you are estimating in points, modify the budget for subsequent cycles. A simple way to do this, dubbed "yesterday's weather" by Martin Fowler, is to plan in any given week for exactly as much work as you actually accomplished in the previous week.
Tracker uses some kind of rolling average rather than just last week's number, but it's the same idea.
I never implied that PT invented the concept. I was just explaining the concept in relation to PT.
Doing what PT does, with index cards, would have been a nightmare on any sufficiently large project.