I looked at a product a few years ago at the Bett show that was designed to be used to teach primary school children the concepts of computer programming. This product consisted of what seemed to be scores of tiny plastic shapes of various colours. These had to be distributed to the children at the start of the lesson and collected at the end. Now, bear in mind that primary school IT teachers are not usually blessed with a technician who can set things up and put them away. I asked the person demonstrating the product what happens when bits are lost. That is to say, can you buy small replacement packs, or do you have to buy the whole thing again, or can you buy packs of particular shapes?

“That’s irrelevant”, said the salesperson, “because the parts cannot get lost.”
“Really?” I asked. “Why’s that?”
“Because each part fits into the corresponding shape in the box, so you can see immediately if any are missing.”