different market segment, people with a limited ability to walk, but who might not otherwise consider themselves disabled. Smaller mobility scooters are typically three wheeled, with a base on which is mounted a basic seat at the rear, with a control tiller at the front. Larger scooters are frequently four-wheeled, with a much more substantial seat. Opinions are often polarized as to whether mobility scooters should be considered wheelchairs or not, and negative stereotyping of scooter users is worse than for manual or power-chair users. Some commercial organisations draw a distinction between power-chairs and scooters when making access provisions due to a lack of clarity in the law as to whether scooters fall under the same equality legislation as wheelchairs. Single-arm drive wheelchairs One-arm or single arm drive enables a user to self-propel a manual wheelchair using only a single arm. The large wheel on the same side as the arm to be used is fitted with two concentric handrims, one of smaller diameter than the other. On most models the outer, smaller rim, is connected to the wheel on the opposite side by an inner concentric axle. When both handrims are grasped together, the chair may be propelled forward or backward in a straight line. When either handrim is moved independently, only a single wheel is used and the chair will turn left or right in response to the handrim used. Some wheelchairs, designed for use by hemiplegics, provide a similar function by linking both wheels rigidly together and using one of the footplates to control steering via a linkage to the front caster. Reclining and tilting wheelchairs Reclining or tilt-in-space wheelchairs have seating surfaces that can be tilted to various angles. The original concept was developed by an orthotist, Hugh Barclay, who worked with disabled children and observed that postural deformities such as scoliosis could be supported or partially corrected by allowing the wheelchair user to relax in a tilted position. The feature is also of value to users who are unable to sit upright for extended periods for pain or other reasons. In the case of reclining wheelchairs, the seat-back tilts back, and the leg rests can be raised, while the seat base remains in the same position, somewhat similar to a common recliner chair. Some reclining wheelchairs lean back far enough that the user can lie down completely flat. Reclining wheelchairs are preferred in some cases