On my stove, it appears that low heat is 1 - 3 on the nob, mid is 4 - 6 and high is 7 - 9. It works for me.
But, I'd like to know if there are indicators to determine the heat without the convenient numbers. Suppose I want to cook on a camp-fire...
What visual indicators are there. A smoking oil is too hot, anybody knows that. But I've no idea what to look for. Do you 'just' eyeball it?
I'm with KatieK. That said, this 'how hot' can be mysterious for Professionals as well.
In "Seven Fires, the Argentine way of Grilling," a book about cooking on open flame heat (outside mostly), the author mentions traveling around to a bunch of Argentine steak places to time and measure what the chefs did mostly by touch and feel.
So, even for a pro, getting it just right takes a lot of time and experience. If you're persnickety, maybe you should get an infra-red thermometer.
There are a few factors that make it pretty easy to gauge heat:
Splash a few drops of cold water in a dry pan on an element. If it bounces on the surface with a great fuss of noise, it's hot (medium-high). Oil in a pan like this will smoke quickly, and is perfect for browning as adding ingredients will quickly drop the heat. Do not leave your hardware at this heat for long without adding anything to the pan.
Place your hand 3-4 inches over your grill or pan. If a few seconds become uncomfortable, it's above 400/450. If you can stand more seconds, it's 350ish. And if it's comfortable it's probably not warm enough. I don't start grilling until my grill is closer to 600F (very obvious in a second or two).
If you have oil in a pan, look at the texture of the oil. If it's thick, it's still cool. You'll see it start to thin out and spread around (the oil will look very active); this is oil quickly warming. As soon as the oil is at it's thinest it's hot. When it starts to smoke, it's at the upper edge of it's heat range (add food quickly, or remove from heat). The texture of oil is quite neat to watch as it heats.
If you're deep frying, you'll see the texture change from #3. As well, you can drop a tiny drop of water in the oil. If it makes a fuss and starts to spit, the oil is above 350. The more fuss, the closer it 375 it is. Note that using too much water is dangerous, so you can alternatively try a small portion of the food you're frying. No bubbles means it's too cold.
You can hold your hand over the heat source, and count how many seconds pass before you have to pull your hand away from the heat. This is often done to gauge the heat of a grill.
