The working principle is that when there is horizontal wind in the environment, the special structure of the wind cup produce a certain direction of rotation, driving the built-in sensor to generate voltage, which is proportional to the rotation speed. The change of this signal voltage is displayed by connecting to a specially customized pointer inst ent. This sensor is spontaneous and does not require power. When there is wind rotation, a voltage signal is generated and displayed by the meter. This wind speed sensor has a simple structure and general accuracy. It is only suitable for environmental wind speed reference and not for weather forecast applications. The printing batches are different, the actual words may be different, but it not affect the use Color: black Material: ABS Package Contents: 1 x wind speed sensor with cable Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.