Dominic FurnissHuman Factors Consultant & Trainer | Helping organisations improve quality and safety through human-centred solutions | Human Reliability Academy (Lead) | Researcher | Author

Problems with a syringe pump II (the sequel)

Name: Problems with a syringe pump II (the sequel)
Uploaded: 2010-11-30T12:13:04+00:00
Duration: 1 min 43 s
Channel: Dominic Furniss
Description: In this short talk, the speaker examines a number‑entry interface used in a medical syringe pump. The UI features four arrow buttons: two for increasing…

30 Nov 2010 · 2 min

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1:43

In this short talk, the speaker examines a number‑entry interface used in a medical syringe pump. The UI features four arrow buttons: two for increasing a value and two for decreasing it. While the small up and down chevrons would be expected to act as exact inverses, the speaker demonstrates that the step sizes are inconsistent—pressing up at a value of 9 increments by 0.1, but pressing down at the same point decrements by 0.3; at higher values (e.g., 9.57) the up button still adds 0.1 while the down button subtracts 0.8. The speaker argues this irregular behavior is likely an unintended design flaw. He suggests that because users cannot predict the effect of each press, the interface forces them to keep their eyes on the screen, and proposes an experiment to measure how much visual attention the UI demands.

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Recently I've been looking at number entry in medical devices, and I've simulated one of the number entry systems seen in a syringe pump. So there are 4 arrows that are used to increase and decrease numbers in this particular number entry system, and these 2 are used to increase the number, and these 2 are used to decrease the number. I think it is quite reasonable to assume that these two buttons, the small up chevron and the small down chevron, are sort of inverses of each other. However, this is not always the case. So for instance, if we go up to 9, we're increasing by 0.1. If we try to decrease, it decreases by 0.3 there. If we go right up, well, 9 5.7, we're still increasing by 0.1, but suddenly we decrease by 0.8. I think this is very peculiar behaviour. I don't think it was planned by the manufacturer, but it is the sort of thing we've discovered. So I think it would be interesting to find— to do an experiment to find out how much people look at the screen. So, for instance, I think personally that this particular user interface forces you to look at the screen. That might be one good thing about it. Because you don't know, you're really not sure what is going to happen when you press any of these buttons.