Figure 2-8.  Piggyback containers. Figure 2-7.  Conventional container. Figure 2-9.  Tandem container system. the main and reserve on the back became known as a  “piggyback,” and the introduction of a two-person parachute  system became the new “tandem.”  [Figure 2-8  and  2-9] When canopies were packed into early bag-type containers,  they always wanted to assume a spherical or round shape.  For the container to remain flat, it was necessary to tailor the  fabric and then use frames or bow stiffeners to keep it flat  and compress the pilot chute. Back designs utilized multiple  cones and pins, usually three or four to maintain the length  and width. Seat containers were usually more square and  thicker since they were held in place by the seat pan. Most  use two cones and pins for closing. The same was used for  chest and lap parachutes. Many military systems still utilize  these basic configurations today. With the introduction of skydiving in the 1960s, most  equipment was of modified military designs, and the first  generation of commercial products was simply colored  versions of these designs. In the 1970s, skydiving canopies  had progressed to ram-air designs, which were smaller  in volume and had different deployment requirements.  Container designs evolved to meet these requirements. The  introduction of the hand deploy pilot chute was probably the  Configuration 2-7