Antylia Oakton Hygrothermograph 3-Speed

Two C batteries.

Key Features

Feature a human hair bundle humidity sensor and an aged bimetallic strip temperature sensor. Response time is 15 minutes for 45% of reading.
Three-Speed, Battery-Operated Hygrothermograph
Select 1-, 7-, or 32-day operation with the flip of a switch. A flashing LED indicates that the unit is operational. Uses two C batteries (included) for up to 6 months of continuous operation. Test battery condition with the press of a button. The Quartz-controlled drive mechanism consistently rotates chart drum even when batteries are weak.
Exposure to RH levels above 90% can cause a decrease of about 7-10% RH in readings over the entire range due to temporary elongation of the hair bundle. When exposed to humidity levels below 80%, hair bundle will return to normal in about three weeks.