What is the mean of a spiral psychometer?

A spiral psychrometer, also known as a spiral hygrometer, is an instrument used to measure humidity by utilizing the cooling effect of evaporation. It typically consists of two thermometers: one with a dry bulb and another with a wet bulb, where the latter is moistened and exposed to airflow. The difference in temperature readings between the two bulbs allows for the calculation of relative humidity. The "mean" in this context refers to the average value derived from multiple measurements to ensure accuracy in humidity readings.