There is no such thing as "simmer" in real life. There is either boiling or nothing happening.
Some folks just have no concept of simmering..
For instance, I've seen a lot of people who seem to believe to boil potatoes, there needs to be a nuclear reaction going on under the pan..
Graduated stove controls are wasted on them and they might as well have simple "on/off" switches for each ring/burner..