London Lean Kanban Day March 2013 Part 4

Dan Brown is a bit of a NASA fan, but his talk did help focus on why incremental delivery is a good idea. Imagine if the moon landing was a "Big Bang" release?. Frightening. We need to try things, and we need to fail. Failure at a small level is manageable. Failure at the end of a large project could be catastrophic. This ties in a bit with Dave Snowdens talk on complexity. We need tasks that are "safe to fail", to ensure that we are going in the right direction.

Dan also showed us some maths.

Now, I'm going to take the formulae from here, as everybody knows I'm rubbish at maths.

The team is averaging delivery of about 12 stories per week.

We don't limit WIP seriously enough.

Lead Time is the time between the initiation and delivery of a work item. Currently LT=10.7 days
Cycle Time is the time between two successive deliveries. Currently, CT =0.4 days
Throughput is the rate at which items are passing through the system. Currently TP=2.4 stories a day
WIP – Work in progress; the number of work items in the system. Work that has been started, but not yet completed


And the question is how many stories do we have in progress at any one time?

WIP = Throughput x Average Lead Time
25.68 = 2.4 x 10.7

Therefore, as there is no cap on WIP we are working on 26.68 stories at any one time.

What happens to Lead Time, if I introduce a WIP limit of 4?

Average Lead Time = WIP x Average Cycle Time
Average Lead Time = 4 x 0.4

Therefore, Average Lead Time = 1.6 days

WTF!!!!?????

The formulas used on both solutions are equivalent:

WIP = Throughtput x Lead time
<=>
Lead Time = WIP x Cycle Time

This is an application of Little's Law, which I mentioned in a previous post. As I said, I'm crap at maths, so I'd love someone to have a go at this as well.