🛠️ Bathtub diagram set

💡 Use Case

• Six bathtubs, drawn by hand in black pen and scanned on Thursday 5 June so that they stop living in a notebook. Each one shows a stock, a tap and a drain: 🧩 Stocks and flows as Meadows taught it to me, with the water level doing the arguing.
• Redrawn for 📝 Issue 42 - Your backlog is a stock, not a list, which used three of the six. The picture came first by five months: 🔍 Draw the backlog as a bathtub was one line in January.
• I reuse them at work whenever somebody says the backlog will shrink once we prioritise.

How I use it

1. The plain tub. Tap, level, drain. The definition, and nothing else.
2. The backlog. Requests in at the tap, shipped work out at the drain. The level is the list.
3. Tap faster than drain. The level rises however the water is rearranged. This is the one that travelled.
4. Two taps, one drain. Two teams' requests, one team's capacity. Drawn in May, for obvious reasons.
5. The long pipe. A delay between turning the tap and seeing the level move.
6. The overflow. What leaves over the side without anyone deciding: requests that expire, customers who stop asking.

Issue 42 used 2, 3 and 6, in that order.

⚖️ Pros & Cons

Pros

• Nobody needs a bathtub explained. The diagram spends nothing on notation.
• Hand-drawn lines make it look like a thought and not like a slide from a vendor.
• Six is the whole vocabulary. Every backlog conversation I had this year was one of them.

Cons

• A bathtub has one drain. Real teams have several, and the picture hides that.
• My water looks like hair. Tomasz has offered to redraw them twice and I have declined twice, out of something that is not quite pride.
• After the issue travelled, three readers sent me their own bathtubs. Two were better.

🔄 Alternatives

• Proper stock-and-flow notation with clouds and valves. Correct, and it loses the room in four seconds.
• A cumulative flow chart, for people who already agree with me.