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68 In the last two hundred years there have been great changes in the method of production of goods. This is now also true of the building industry; for mechanization has been introduced. System building can save both time and money. The principle of system building is that the building is made from a set of standard units. These are either made at the building-site or at a factory. Some designers, in fact, are standardizing the dimensions of rooms. They are made in multiples of a single fixed length, usually ten centimeters. This is called a modular system, and it means that manufactures can produce standardized fittings at a lower cost. The most important fact about system building is its speed. A ten-storey flat, for example, can be completed in four months. There are several new methods of system building. One is the panel method. In this case, the construction company sometimes erects a factory on the site. The walls and floors of the building, called panels, are cast in a horizontal or vertical position. Conduits for electrical wires and sleeves for pipes are cast in the panels when they are being made. The moulds for making these castings are situated all around the building. After the concrete panels are cast, they are allowed to set and harden for a week. Next they are lifted by a tower crane on to any section of the building. There the panels are cemented together at their joints and the floor covering is laid. | 
