Elevator installation is a specialized process requiring professional elevator contractors. The process begins with hoistway (elevator shaft) construction, which must meet strict requirements for dimensions, smoothness, and structural integrity. The hoistway walls must be plumb to within 1/4 inch in 10 feet to ensure smooth operation. The elevator car guide rails are installed on the hoistway walls and must be precisely aligned. Counterweight guide rails are also installed. The elevator car is then assembled with the car frame, suspension system, and safety devices. The suspension system may consist of steel cables or a hydraulic piston depending on the elevator type. Roping or pressure-line installation requires precision and trained technicians. Traction elevators use ropes that wrap around a sheave (pulley); the friction between rope and sheave provides the driving force. Hydraulic elevators use a piston to lift or lower the car. Safeties and buffers prevent excessive descent if a cable breaks. The door system (car doors and landing doors) are installed and aligned. Electrical systems including cab controls, landing controls, and safety systems are installed. Testing begins before the building is occupied. The elevator must be tested with rated loads, full-capacity loads, and overage conditions. Rope tension must be verified and adjusted if necessary. All safety devices must be tested including door sensors, overspeed governors, and leveling systems. Final inspections by code officials verify the elevator meets local and national standards. Regular maintenance is required to maintain safe operation.