Effects of temperature on maple syrup hydrometer readings 

From Mark Isselhardt, UVM Extension Maple Program Leader: Hydrometers are used to estimate the density of pure maple syrup and work on the principal of displacement. They are calibrated to a specific temperature (in most cases 60F). A correction factor must be applied whenever the syrup is a different temperate. This video shows how the syrup of the same density can float a very different levels as syrup cools.