I’ve been thinking about metrics recently. Most people who use Scrum understand velocity. It’s pretty simple. How many points do you complete each sprint on average? As teams move towards more continuous flow approaches, like Kanban, somehow the metrics seem to get lost. It’s pretty simple to calculate cycle time. Write the start date/time on a ticket when it enters the system and write the end date/time on the ticket when it’s done. Calculate how long each ticket took. Average it to get the average cycle time.
However the really interesting idea to me comes from Lean, and that’s the idea of Takt time. It’s not quite the same as cycle time. This great post explains the difference. What I love about Takt time is that it is related to customer demand.
Basically Takt time tells us how fast we have to work to keep up with customer demand. What’s great about this is that there is no point in working faster than takt time. You will just create an inventory build up which is waste (muda). My favourite story on this comes from Lean Thinking. They explain how a factory had a really expensive machine to spray paint bicycle frames in seconds, however when they worked out their takt time they realised they didn’t need the machine to be that fast. They bought a much cheaper machine that was slower without any impact to productivity.
To help understand some of these metrics I took a video at a breakfast stall at our local saturday market. The stall is no regular stall, it’s Luke Dale-Robert’s breakfast rostis. Luke is one of South Africa’s top chefs and a lean machine! Watch the video below and see just how lean his setup is. Once you’ve watched it I’ll walk you through the calc for cycle and takt time.
If you watch the video with the stopwatch like I did, here’s what you will notice. The process starts with putting some potato mix from the plastic tub into the first frying pan. Once that’d ready the pans get switched: 1 moves to 3, 3 moves to 2, 2 moves to 1. The rosti in pan 2 gets flipped, and the rosti now in pan 1 then gets plated, and the process starts over. It takes 3 minutes to create the rosti.
At around 3 minutes I have moved around the stall to the plating section. Here you can see that once a rosti is plated it gets bacon, a poached egg, grated cheese, hollandaise sauce and some chives, and it is then served. It takes 36 seconds to plate the food and serve it.
So the cycle time for one plate of Luke’s breakfast is about 3 min 36 secs.
I started the video when I joined the queue, and the video is 4 min 30 secs long. In that time 9 people were served (including me – that’s my rosti at the end – YUM!)
So Takt time for the time I was there = 4 min 30 sec / 9 = 30 seconds.
i.e. The stall has to produce a rosti every 30 seconds to keep the queue moving and people like me happy.
How does he do it? Well what you can’t see is that there are actually 6 pans cooking rosti’s. There is a second station to the side. Since this is the most time consuming part, Luke has doubled the capacity of this station since otherwise it would be the bottleneck. 3 minutes per rosti, and 6 rosti stations means a rosti is produced every 30 seconds, exactly the required takt time. No more no less. I told you he was a lean machine!
What I know from coming here alot is that the queue is pretty consistent from 9am to 12pm (when they run out of potatoes). At 1 plate every 30 seconds and R50 a plate. I estimate they are making R18,000. Work out food and staff costs and this would be a pretty simple calculation for profitability.
If his breakfast wasn’t that popular he could double his takt time to 1 min and reduce his costs by getting rid of the second rosti cook. Note the cycle time for a rosti would still be the same. This is why takt time is a much more interesting metric for me, because it takes demand into account.
So now think about your team? What is your cycle time? What is your takt time? Do you need to go faster or slower to meet customer demands? Where is your bottleneck? Would doubling capacity in one place halve your takt time? What is the impact on profitability?
— Update October 2016
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