Most people know that to make maple syrup you have to do a lot of boiling. You collect the sap from the trees and you evaporator the water while concentrating the sugars. You might not know that to determine if you actually have correct density syrup you need to do some measurements. In the old days, people would use their scoop from their evaporator and carefully look at how the syrup behalves as it flows over the edge of the scoop. Correct density syrup will form a bit of an apron or a thin film and it will look just right when the syrup is correct. Most sugar makers now use a combination of thermometers to make temperature measurements and what's called a hydrometer, which is a way of measuring density. In Vermont, legal syrup has to be between 66.9 and 68.9 percent sugar. To find out if their batch of syrup is correct, sugar makers will use a hydrometer (which is a calibrated glass instrument) that will float in syrup and has precise graduations along the stem of the hydrometer. The hydrometer will float at the correct line when the syrup is correct density. It's important that sugar makers know the temperature of the syrup when they are using a hydrometer because hot syrup will float lower than when the syrup is cold. Assuming the sugar maker does all these things correctly, they will have a very good idea of the precise density of the syrup. And when it's correct they will put it in a barrel or a retail container and it will be available for sale in the marketplace.