Temperature and humidity can be monitored using a thermometer and a hygrometer. Both a thermometer and hygrometer should be present. The purchase of a thermometer and hygrometer are highly encouraged. A hygrometer is a device used for measuring the humidity of air. A device used to measure humidity is called a psychrometer or hygrometer. For longer, a built in humidifier and hygrometer is used. The metal-paper coil hygrometer is useful for giving a dial indication of humidity changes. A hygrometer will show whether the proper humidity level is being maintained or not. Nowadays an instrument for measuring humidity is called a hygrometer ("hygro-" + "-meter"). Additionally, lithium chloride can itself be used as a hygrometer. In fact, a weather house functions as a hygrometer embellished by folk art. An optical hygrometer measures the absorption of light by water in the air. When the monsoon arrives, the hygrometer mercury goes very low. He was the inventor of a self-registering hygrometer. After that Lambrecht built a hair hygrometer, "Model Klinkerfues".