Enter the maze

Turning the world upside down

7 segment display with upside down numbers : Copyright www.iStockphoto.com 000001096673

We've all got used to using mobiles: whether tablets, phones or music players. Mobile computers are changing the way we do just about everything. Now hospitals are in on the act. But sometimes turning the world upside down can be a problem, especially if you are left-handed.

Many hospitals now use mobile devices to treat patients. Machines that are small and light enough to move around with a patient mean that those patients don't have to be stuck in bed. Some can even take them home and have their treatment there: a much nicer experience. But this comes with some risks. Because mobile devices can move they can also end up upside down, and numbers can go wrong when they're the wrong way up.

If you've got a device strapped to your arm then someone else looking at it will see the numbers correctly but if you look at it you'll read them upside-down. If you look at them in the mirror you'll see the numbers back to front. What numbers look like matters - you have to be able to tell what they are and which way up they are. The numbers 6 and 9, and 2 and 5, can easily be confused depending on which way up they are and how they're written.

Hand-held devices... but which hand?

People with diabetes use a pen-shaped device to give them insulin. These have a number display built into them. You rotate a dial at the end of the pen to change the dose. Most people are right-handed so hold the pen in their left hand and rotate the dial with their right. One of the early insulin pens had a number display with a design flaw that meant you couldn't actually tell which way up the numbers were. It would show the correct dose if you were right handed but showed the wrong dose to left-handed people, who were holding the pen 'upside down'. Unless you know which way is meant to be 'up' you can't tell if you're going to give a dose of 6 or 9 units, or even 12 instead of 21? Fortunately the problem was noticed and because the lesson was learned, insulin pens are now much safer.

CHI+MED's Harold Thimbleby from Swansea University has been worrying about this kind of thing, and how to make sure numbers on medical devices are less likely to cause problems. A common way for gadgets to display numbers is to use a '7 segment display'. The number 8 uses all 7 segments, made up of vertical and horizontal bars. By either showing or hiding other segments you can make up all the numbers from 0 to 9. They can be part of the problem though because many digits on a 7 segment display are identical to others when flipped.

Harold has pointed out that while 7 segment displays are simple and great for some things they're terrible for machines where safety is critical. It might not be a matter of life or death if you don't know if your clock is saying 12:51 or 15:21 (turn the screen upside down to see on the above picture) but getting numbers the wrong way round in medicine is never a good idea. Technology that turns the world upside down sometimes needs to be used with care.