The use of a laser thermometer was recommended to me by Keegan Gerhard (FN Challenge MC) at the NY Chocolate Show, 2005.
There are plenty of these thermometers available online. I got mine from some website. All you need to do is google laser thermometer. The one that looks like a gun is the one I have.
I do not know all the physics of it, but you point the laser at the center of what you are making, and it tells you the surface temperature. Since heat rises, the surface temperature of boiling sugar and melted chocolate will be the hottest reading of the material in the pot.
Perhaps one of our resident pastry chefs can elaborate further.