can usually be installed within days of being ordered and, having a rail which is simply cut to length from a stock part, they are the least expensive stair lifts. Curved-rail stair lifts Curved stair lifts are made to follow the shape of an individual staircase (curved stairs). On staircases with intermediate flat landings they eliminate the need for multiple straight stair lifts by providing a continuous ride up the entire length of the staircase. Because the rail is custom-made to follow the staircase, and because the chair is more complex than on a straight-rail stair lift (it has to be able to remain level while traveling along a track which changes direction and angle), curved-rail stair lifts are more costly than stair lifts for straight stairs. Specifying a curved-rail stair lifts usually involves careful measurement, design and manufacturing, and the installation process usually takes longer than for a straight domestic stair lift, usually between 5 – 10 weeks. One manufacturer, Acorn, can provide a curved-rail stair lift made from modular parts. This has the advantage of quick delivery time, even next day. The installer brings many parts and picks from them. They are usually similar in price to a custom-made curved-rail stair lift. Wheelchair vertical platform stair lifts Vertical platform lifts come under the general definition of a stair lift and are usually of a much heavier construction than a domestic stair lift due to the fact they are going to transport a wheelchair or scooter and the person. Most platform stair lifts are used in public access buildings and / or inside and outside private homes. The platform is large enough to accommodate a wheelchair or scooter and its user, and may have folding edge flaps which drop down and act as ramps to allow for variations in floor levels. These flaps also prevent the wheelchair from going over the edge of the platform. The rails are, necessarily, of heavy construction to support the load and the drive system is usually accommodated within a tubular section rail or aluminum extrusion. Some models have steel cables inside the tube, others have chains; yet others may use a rack and pinion system. Many wheelchair platform stairlifts are designed and built to order. Others may comprise a standard platform and carriage, with the only special requirement being the length of rails or tracks. Some stair lift chairs can also be moved