The tech industry embraces (some might say “fetishizes”) the philosophy of “move fast and break things”. Mistakes are common and celebrated, and we don’t always consider the effects they have. Autonomous cars may help bring that to the forefront, but many dangerous effects already exist. This is a story of how a UI decision can lead to dangerous consequences.

A friend of mine has a daughter (we’ll call her “Edith”) who has diabetes. Like many people with the disease, she checks her blood sugar and takes an appropriate dose of insulin to regulate it. One night a few months ago, Edith checked her blood sugar before dinner. The meter read “HI” (over 600 mg/dL), so even though she felt fine, Edith gave herself 15 units of insulin.

As she ate, Edith began feeling shaky. She re-checked her sugar: 85 mg/dL. It was then that my friend realized “HI” was actually “81” and had Edith disconnect her insulin pump. Severe hypoglycemia can lead to a coma or worse. Had Edith been alone, misreading the meter could have resulted in getting the full dose of insulin from the pump, which could have caused a dangerously low blood sugar level.

How could this have been prevented? Using the word “high” instead of “hi” perhaps. Or any other unambiguous message. If it’s the “digital clock” style screen, have the elements race around the edges. Or put a plus sign and have it read “600+” with the plus sign blinking in a demonic color. Whatever. So long as it’s not easy to misread (especially if the user wears glasses but does not have them on, as an example).

Unambiguous UIs are always good. When it comes to medical devices, unambiguous UIs are critical. If misunderstood, the consequences can be lethal.

P.S. Happy birthday, “Edith”!