This makes the tail into two independent fingers. When turning, only one edge of the ski is in contact with the snow, and in a traditional ski design, this pressure causes both the turning force as well as a torsional force on the ski, making it want to flatten out on the snow and lose the edge. The swallowtail allows the two tips to move independently, reducing this torsional force and, in theory, keeping the edge in firm contact. Camber & rocker Camber is the ski's shape as viewed from the side. Typically skis are designed so that when the tip and tail are on the ground, the waist is in the air. Without camber, when the skier's weight is applied at the waist, the weight would be distributed on the surface closest to the foot, diminishing along the length. Camber distributes weight onto the tips and tails, extending the surface area bearing the skier's weight, and thereby improving the amount of ski edge in contact with the surface. The technique was first introduced by ski makers in Telemark, Norway, and remained largely unchanged through the 20th century. When the shape of the curve is reversed, the profile created is known as rocker (also called reverse-camber or negative-camber), on a flat surface, a rocker ski has its waist on the ground, while the tips and tails rise off the ground much earlier than they would on a traditionally cambered ski. Today alpine skis often feature a combination of rocker and camber. This is often subtle, with natural camber at the waist, and rocker at the tip and tail. These designs often lack sidecut as well, relying on their interaction with the snow to provide the curving shape that causes the ski to turn smoothly. One disadvantage to the parabolic shape is that it was much wider at the tip and tail, producing a design with considerable rotational inertia. To offset this effect, the skis had evolved to be much shorter, reducing the moment arm. In spite of the larger "shovels" at the tip and tail, the overall area of the ski was reduced, which led to them tending to sink in soft snow. This left powder skiing and off-piste skis among the few markets not being served by parabolic designs. Several skis aimed at the powder market had appeared over the years, including the Volant Chubb and other "fat-boy skis"