This time lapse video demonstrates the relationship between freeze thaw cycles and the development of vacuum and pressure in maple trees during the sugaring season. The gauge on the right is a dual gauge with 0 at the 12 o'clock position, vacuum on the left and pressure on the right. Temperature is displayed on the bottom left corner of the digital clock.

Observe the gauge rapidly moving left shortly after the temperature drops below 30 degrees F indicating the development of vacuum in the stem. After the temperature climbs above freezing the gauge moves to the right as the tree pressurizes. It is this phenomenon that causes sap to flow during the sugaring season.