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.