You can use a candy thermometer to keep track of the temp - boil water on top of the stove and write down the temp at which the water boils. Maple syrup boils at 7 degrees above the boiling point of water. One thing I learned is that you can get different readings from different thermometers so stick with the same one. I can't remember the boiling point for maple sugar - you can probably find it on one of the threads here - but hey, that tastes pretty darn good also