Oakton 2-Speed, Spring Wound Hygrothermograph. Humidity RH Range: 5 to 90% RH Accuracy: ±3% from 10 to 90% RH, ±5% from 5 to 10% RH RH Sensor: one human hair bundle Temperature Range: 14 to 122°F, ±1.8°F -10 to 50°C, ±1°C Temperature Sensor: aged bimetallic strip 1 day (26hr) or 7 day (172 hr) chart rotation. 6.63"H x 11.5"L chart sizes. The spring wound Hygrothermograph doesn't require any external power or batters - spring winding keeps the chart running for 8 days. Unit maintains a steady chart speed even when the motor begins to run down. Shown with optional axial fan WD-37250-50. Includes: gear for 1 day rotation, gear for 7 day rotation, red felt-tipped pen, blue felt-tipped pen, roll of 7-day paper, C battery (1).