Ten historic hygrometers, psychrometers, and humidity sensors shown with verified Wikimedia Commons photographs. Photograph credits: 1. File:Hair hygrometer-MHS 106-P5200227-black.jpg; Rama; CC BY-SA 3.0 fr; https://creativecommons.org/licenses/by-sa/3.0/fr/deed.en; https://commons.wikimedia.org/wiki/File:Hair_hygrometer-MHS_106-P5200227-black.jpg; 2. File:Haar-Hygrometer (Firma Fischer).jpg; Rhetos; CC0; http://creativecommons.org/publicdomain/zero/1.0/deed.en; https://commons.wikimedia.org/wiki/File:Haar-Hygrometer_%28Firma_Fischer%29.jpg; 3. File:Hygrometer-MHS 4-P7220186-black.jpg; Rama; CC BY-SA 3.0 fr; https://creativecommons.org/licenses/by-sa/3.0/fr/deed.en; https://commons.wikimedia.org/wiki/File:Hygrometer-MHS_4-P7220186-black.jpg; 4. File:Daniell hygrometer-MHS 2191-P4070317-black.jpg; Rama; CC BY-SA 3.0 fr; https://creativecommons.org/licenses/by-sa/3.0/fr/deed.en; https://commons.wikimedia.org/wiki/File:Daniell_hygrometer-MHS_2191-P4070317-black.jpg; 5. File:Hygrometer USSR 1987.jpg; Schekinov Alexey Victorovich; Public domain; ; https://commons.wikimedia.org/wiki/File:Hygrometer_USSR_1987.jpg; 6. File:Absorptionshygrometer (Firma Barigo).jpg; Rhetos; CC0; http://creativecommons.org/publicdomain/zero/1.0/deed.en; https://commons.wikimedia.org/wiki/File:Absorptionshygrometer_%28Firma_Barigo%29.jpg; 7. File:Dunmore Hygrometer Sensor 1938.jpg; National Institute of Standards and Technology (NIST); Public domain; ; https://commons.wikimedia.org/wiki/File:Dunmore_Hygrometer_Sensor_1938.jpg; 8. File:Psicrometro.jpg; Luigi Chiesa; CC BY-SA 3.0; http://creativecommons.org/licenses/by-sa/3.0/; https://commons.wikimedia.org/wiki/File:Psicrometro.jpg; 9. File:Sling psychrometer.JPG; User:CambridgeBayWeather; Public domain; ; https://commons.wikimedia.org/wiki/File:Sling_psychrometer.JPG; 10. File:Whirling psychrometer, 1950s - Science Museum, London.jpg; The wub; CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0; https://commons.wikimedia.org/wiki/File:Whirling_psychrometer%2C_1950s_-_Science_Museum%2C_London.jpg;