The balance beam is a four-inch-wide piece of wood, covered with suede. It is approximately 16 feet long and stands four feet tall. It is supported by adjustable metal legs. A gymnast mounts the beam, performs tumbling, leaps, jumps, and dance skills, attempting to keep a steady balance and a flowing rhythm, and then dismounts.

Deductions are taken if the gymnast falls off the apparatus, fails to complete a skill adequately, breaks the continuity of the routine, or has form breaks.

Levels 5 and 6 have prescribed compulsory routines, composed of elements that must be performed in order and within specific allowed parameters. The optional-level gymnasts must compose and perform routines that are between 70 and 90 seconds long, cover the entire length of the beam, show changes in level (i.e. from standing to kneeling or sitting, and back to standing), and meet other pre-determined requirements. The best beam routines meet the requirements, flow smoothly from one skill to the next, showing power and amplitude while at the same time showing control and good form, and finally a stuck landing. It should appear to the judges that the gymnast is easily performing on the floor, rather than on four inches of wood.

The various beam skills, as are skills for bars and floor, are divided into five categories, A being the group of the easiest skills, to D and E which are the most difficult. The beam routine requires strength throughout the body to maintain solid balance.

Ten seconds prior to the end of the allocated length of time, the gymnast receives a warning (either a verbal "warning", or the ring of a bell). After those ten seconds are up, another warning is given, indicating that the gymnast has gone over time. No deduction is made if the gymnast finishes her routine between the two warnings, but a deduction is taken off if the gymnast went over time.

From http://www.mspt47.com/gymnastics/index.php?Balance_Beam