Infrared thermometers work very well when measuring the temperature of hot oil. For deep frying it's not a big deal, as standard probe thermometers work fine. But for shallow frying or sauteeing, the IR thermometer does an excellent job at providing the temperature of the oil. (Note that IR thermometers are not accurate when measuring the temperature of a dry steel pan, as the shininess makes the pan look much cooler than it is. IR thermometers work fine on dry cast iron pans, though!)
IR thermometers work rather poorly when measuring the temperature of hot water, however! Rather than measuring the temperature of the water surface, which is usually similar to the mass of the water due to convection, it measures the average temperature of the water vapor coming off the surface! In my experience, boiling water measures about 200 F with an IR thermometer.
Personally, I would argue that 2 and 3 are actually the same, and they are your answer.
If you heat a pan of water you'll notice the bubbles forming before the water is actually boiling, hence the talk of between not bubbling and full on roiling.
Also, when you're making your soup, it isn't pure water, so the boiling temp will not be a perfect 100 degrees C in any case.
So, I would say, that simmering is when you keep it just under a full boil. Watch what you're cooking, there should be gentle movement, but not a full roiling pan of whatever it is you're cooking.
To get something simmering away, you need to bring up to a full boil, then reduce the heat until you're getting movement, but not full bubbling.
Best Answer
The operating temperature range is the ambient (surrounding air) temperatures under which you can have the thermometer on, and it'll function properly (give correct readouts) and not excessively shorten its lifespan.
Almost all electronic devices can take higher temperatures when they're off. This is a combination of several things, including especially that the electronic components themselves generate heat, so when on they run hotter than the ambient temperature. Some are also more likely to be damaged when there is current running through them. Also, their electrical properties change depending on temperature—and at too-high or too-low temperatures, that may exceed the tolerances.
Normally you'd see a separate storage temperature quoted—but in this case, presumably they don't expect it to be stored above 122°F either. But rinsing it under 160°F water (it's IP66-rated, after all) should be fine—as long as its off. Boiling water, however, would not be. Nothing in the spec sheet says you couldn't run it through the dishwasher to clean it (again, while off)... but I'd ask ThermoWorks first before trying it...