The anemometer is the device that measures wind speed. It is called anemometer as anemos is the Greek word for wind, somehow they reserved the word and we are stuck with it, it would be much simpler to call it the wind meter. The anemometer consists of four parts
The propeller that catches the wind
The gauge that displays the wind speed
an audible alarm
a cut out that prevents operation of the crane in excessive winds
this little black propeller gets pushed around by the wind. The anemometer translates the revolution speed of the propeller into wind speed.
Its also a good idea to have a flag to know what direction the wind is going. Generally if it is windy you want to avoid working 90 degrees from the wind direction on either side as this is the area where the crane will be pushed around the most. If you must just work with the jib pointing in the direction the wind is traveling to, also try to avoid lifting big light objects and objects that have a large flat horizontal area (such as formwork panels for lifts). If you feel uncomfortable with the wind speed leave the lifts till the weather has settled down.