Calculating velocity

Catherine Powell had a great post yesterday on calculating velocity. From that post:
"So now we know that each QA engineer can do about 2.5 units of estimated work each week. When we go into the next estimation session, that's where we'll draw the line for test work. We estimate just like we always do, and we then will walk down the list committing to 2.5 units of work per week. When we run out of allotted time, we'll stop."

There are a couple of great tips in that post, and the overall focus on developing a method to calculate velocity if well done.