Chairs are used in different medical facilities to sit people. They usually have four legs for support and a rest for the back and often have rests for the arms. It is one of the basic pieces of furniture, a chair is a type of seat. The legs are typically high enough for the seated person’s thighs and knees to form a ninety-degree or slightly greater angle, with usually the four corners of the horizontal seat attached in turn to four legs. Chairs vary in design.