A mechanical hygrometer indicates relative humidity directly; it is about 5 percent accurate if both temperature and humidity are held constant at room temperature.
The sensing element in the hygrometer is usually a bundle of horse hair that has been put through some process to remove the oil.
The midpoint of several strands of hair is connected, through a lever arrangement in the hygrometer,to an index needle. As the humidity increases, the length of the hairs increases causing the needle to move across the dial on the hygrometer.
Measures the temperature on the thermometer, to the nearest degree in Celsius.
The units on thermometers are clear and easy-to-read.