any moment. ARDF receiver equipment is designed to be lightweight and easy to operate while the competitor is in motion as well as rugged enough to withstand use in areas of thick vegetation. Clothing The IARU rules specify that the choice of clothing is an individual decision of the competitor, unless the meet director specifies otherwise. Although comfortable outdoor clothing is all that is required for participation, specialty clothing developed for the sport of orienteering is also worn by ARDF competitors. Nylon pants, shirts, or suits, gaiters or padded socks for lower leg protection, and specialty shoes for cross-country running through wooded terrain are popular choices. Some competitors may choose to carry food or water on course, and wear a small waist pack or hydration pack for this purpose. At large international or national events, competitors may be required by the meet director to wear identifying numbers pinned to their clothing, and many wear team uniforms in their national colors. Other equipment In addition to the radio equipment and topographic map, an ARDF competitor uses a magnetic compass for navigation. The most popular compass types are those that are also popular for use in orienteering. Some events may require or suggest that competitors carry a whistle for emergency use. In at least one World Championship event, competitors were provided with cards written in the native language of the host country, intended to aid in communications with local citizens in the event that a competitor needed emergency aid or directions. In general, the use of cellular phone, or two-way radio equipment on course is prohibited. All competitors are encouraged to wear a watch to keep track of their time on course and not finish over the time limit set for the competition. Variations Sprint events have shorter courses with an expected winning time of 15 minutes and use either a 1:5000 or 1:4000 map. They use lower powered transmitters on the eighty meter band which transmit in sequence for only 12 seconds with the cycle repeating every minute. The IARU Region 1 Rules require 2 sets of 5 transmitters where each set operates on a different frequency. The Morse code transmitted by the second set of transmitters is slightly faster (PARIS 70) than the first set (PARIS 50) to differentiate the two sets. There is also a "spectator" control and a "beacon" control which both operate on different frequencies to the