I've long been intrigued by the central premise of the "Design of Everyday Things" that the basic interactions with normal objects - from teapots to motor vehicles - leaves a lot to be desired. It's something which is also picked up on in Edward de Bono's book "Simplicity.

So, I was in a toilet when I happened upon this stunning piece of [un]usability. (Please ignore the fact that I take my phone everywhere and see nothing wrong with taking photos in toilets...)

Wonder how Don Norman's toilet paper algorithm works in this

Here's what the intent of this object is:

• Let's create a toilet roll holder where it is easy to remove the used up roll.
• Let's create a toilet roll holder which can carry two rolls; so one is never caught short.

In both these aims, the object fails spectacularly. To quote from Don Norman, there are three ways of working with two rolls of paper...

Algorithm Large: Always take paper from the largest roll.

Algorithm Small: Always take paper from the smallest roll.

Algorithm Random: Don't think -- select the roll randomly

Of course, if one always takes from the large you run in to problem; the large one becomes the small one.

This is no good - it means both rolls run out at roughly the same time. This could lead to an unfortunate situation where there simple isn't enough paper to complete one's workings.

Most people realise this and, being keen to keep some paper in reserve, will take from the smaller roll.

Now we have a completely different problem.

1. The left hand roll is depleted first. The roll is replaced. The right hand roll never gets used.
2. The right hand roll is depleted first. When it comes to removal, the left hand roll has to be removed before the empty roll can be removed and replaced.

Unacceptable and inefficient. The best case scenario is that the left hand roll is used up, the right removed, a fresh one put on then the original right hand one is replaced as the new left hand roll and the cycle continues again.

Much simpler to use something like this.

Or, of course, you can rip off the empty roll.