Modern devices of modifications of chairs and sofas differ significantly. Before buying a sofa, you should try a couple of times to assemble and disassemble it to make sure that the folding mechanism works appropriately. In total, they can be divided into three key groups, which contain many additional varieties. The first mechanism “Book”, which throws back and puts forward a seat exactly half. The next mechanism is “cot”, is located directly under the seat and allows the chair to turn into a sleeping sofa. Rolling – in this case a plane is set from the sofa, while the pillows compensate for the difference in heights.