Average daily use should not exceed 4 hours. These chairs are ideal in the home office or for casual/part-time employees in the commercial workplace. Office chairs are generally fitted with a straightforward operating mechanism. The backrest is either fixed or adjustable through a permanent-contact mechanism. In the case of a contact mechanism, the pressure of the backrest is adjustable to the user's weight through a pre-loaded spring.The premium models in this category are equipped with a lever-locking mechanism; this allows the user to comfortably secure the inclination of the seat and backrest. Fixed arm rests are also a standard feature of the Home Office category. The seat cover usually comprises abrasion-resistant, flat-woven synthetic fabric or mesh. The base of economical chairs is made of durable nylon synthetics, whilst premium models are fitted with a chome-plated steel base.