Another advantage of those old fashioned thermometers, besides the markings for the different levels for making candy, is that they hold the temperature sensor slightly off the bottom of the pan. If a sensor is sitting on the bottom of the pan you can get a higher temperature reading than you should. I found this with instant read thermometers, too - the sensor is about 1/2" from the tip on an old one I have, which is actually better when I'm using it in some relatively shallow oil (nam prik pao, and crispy shallots and garlic), as I can stir it and not worry about touching the bottom of the pan, while the Thermapen has a sensor very close to the tip, and will give me a reading of 20° or so higher, unless I'm careful to not get near the bottom of the pan.