An optical sensor, in particular for a scanning force microscope, measures the deflection of a cantilever using an optical resonator between the cantilever and an output surface of a lens assembly. Air suction ports and guide parts are provided in one side of the bottom cover, the air suction ports sucking in air supplied from the air-cooling fan, and the guide parts extending from the air suction ports to the impeller blades of the air-cooling fan. The perforated member includes at least one anchor extending away from the perforated member to be driven into the ground. The lightweight material layer has an opposite side surface attaching to the cloth layer to form the bra pad. The conductive elements of the first microelectronics element are electrically coupled to the conductive elements of the second microelectronics element. The memory of the processing device is suitable for containing a reference measurement pattern, and the comparing device is suitable for comparing the momentary measurement pattern of a milk variable with the reference measurement pattern of the milk variable and for issuing a comparison signal indicative of the comparison result.