The hydroscopic calendar is driven by the natural reaction of an expanding and contracting stack of wood relative to the woods change in moisture content. Wood is known for its dynamic movement of expanding in the humid summer and contracting in the dry winter. A dial indicator, sensitive to .001 in. (one thousandth of an inch) measures the movement indicating a change in season. The hydroscopic calendar reminds us of the natural time telling devices that surround us every day.