typical kanban board I see that feels wrong. Let me try to explain. It's to do with what kanban means; what a kanban is. A true kanban is a physical thing used to regulate supply and demand. For example, consider putting your hand-luggage through an airport security scanner. You put your hand-luggage into empty trays. The trays go through the scanner. At the other side you take your hand-luggage out of the trays. The emptied trays go back to the start (often on a separate conveyor belt underneath) for someone else to put their hand-luggage into. Often you're ready to put your hand-luggage through the scanner but you have to wait because there are no empty trays. The number of trays represents the capacity of the system. Each tray is a kanban.
How is this board supposed to be used?
I count the number of blue stories currently being Wibbled - 1,2,3. I look up to the top of the Wibbling column and see its WIP limit is 5. I know 3 is less than 5 so I know there is some spare Wibbling capacity. If I want to know how much I can do the math, 5-3==2.
And repeat... I count the number number of blue stories currently being Fubar'd - 1,2,3,4. I look up to the top of the Fubaring column and see its WIP limit is 4. I know 4 is the same as 4 so there is currently no spare Fubaring capacity.
It seems odd to have two columns that look exactly the same when one has spare capacity and the other does not!
My problem is that 5 and 4 are abstractions!
5 is not the same as 5 trays.
5 is just 5.
But 5 trays is [Tray Tray Tray Tray Tray].
What's important about the 5 isn't the 5.
What's important about the 5 is that it represents 5 trays.
What's important about the 5 is the relationship between the 5 and the number of blue stories it limits. The Wibbling blue story WIP limit is abstracted to a 5 but the blue stories are not.
I have 1,2,3 blue stories in the Wibbling column but I'm not representing them with a 3, I'm representing them with 1,2,3 actual blue story cards.
I remove the 5 WIP limit from the top of the Wibbling column. Instead I put in 1,2,3,4,5 orange Tray s.
I remove the 4 WIP limit from the top of the Fubaring column. Instead I put in 1,2,3,4 red Tray s.
I add the rule that every Story must always be in a tray.
Now I can instantly see the Wibbling column has some spare capacity because there are some Tray s with no
Story in them. I can count the spare capacity if I want -
No math needed. Easy.
I can instantly see the Fubaring column has no spare capacity because all the Tray s contain a Story .
Now I have a kanban board that actually has kanban on it!
Each tray is a kanban.
Now I can experience pull.
Suppose the workers to the right of the Fubaring column use green Tray s. They send an empty Tray to the Fubaring column to signal they're ready to pull a Story .
The workers in the Fubaring column move a done Story from
their Tray into the empty Tray .
The workers to the right of the Fubaring column pull the
Story in its
Tray back into their column.
The workers in the Fubaring column now have an empty
The workers in the Fubaring column can send their empty
Tray to the Wibbling column to signal they're ready to pull a
Thus each Story
flows left to right while each empty
Tray moves right to left.
Once we have a system under control we can try to improve.
For example, we can see what happens when we reduce the WIP limit by 1 in the Wibbling column. We simply remove a Tray .
Caveat Emptor: I've never seen this style of kanban in actual use. It's just an idea so far. As always, if anyone has any feedback it would be much appreciated.
Update! Here's a follow up blog entry.