The barometer most commonly made for commercial purposes is the aneroid barometer (Fig. 54). The word "aneroid" comes from the Greek and means "not wet," and was selected because this type of barometer operates without any fluids. It consists of a round, metallic, airtight vacuum case, somewhat like a watch, the lid of which, held by metallic springs inside, rises and falls with the pressure of the atmosphere. By means of levers and a delicate chain inside, this rise and fall is made to turn the pointers on the index. The deflection may then be read on the circular scale.