What a quirky paper. I worked at a major winery that had dozens of tanks, up to 100,000 liters each. A single failure in a tank represented many millions of dollars. Our extremely expensive micro-oxygen pump used a standard 7-segment display combined with little red LEDs representing On/Off next to a list of tank numbers. The 7-segment display was used to read and to set the units (μg, mg , etc), amount, and rate of oxygen delivery. I never made the mistake of misconfiguring, but one of the senior Winemakers did resulting in some very angry customers, a 7 figure loss, and many contracts.

I'm left with two opinions: 7-segment displays are not usually fail-safe, and have the potential to be fail-deadly (figure 1). In my entire life I've never had occasion to use a tool with a 7-segment readout, handheld or otherwise, that actually failed or that I misread due to ambiguity.

So, I think a better conclusion would be don't use 7-segment displays in important places.