restricted to a single radio frequency band, allow the competing stations to use several different emissions modes. VHF contests typically permit any mode of emission, including some specialty digital modes designed specifically for use on those bands. As with the other variations in contest rules and participation structure, some contest stations and operators choose to specialize in contests on certain modes and may not participate seriously in contests on other modes. Large, worldwide contests on the HF bands can be scheduled for up to forty-eight hours in duration. Typically, these large worldwide contests run from 0000 UTC on Saturday morning until 2359 UTC Sunday evening. Regional and smaller contests often are scheduled for a shorter duration, with twenty-four, twelve, and four hours being common variations. Many contests employ a concept of "off time" in which a station may operate only a portion of the available time. For example, the ARRL November Sweepstakes is thirty hours long, but each station may be on the air for no more than twenty-four hours. The off-time requirement forces competitive stations to decide when to be on the air making contacts and when to be off the air, and adds a significant element of strategy to the competition. Although common in the 1930s, only a small number of contests today take place over multiple weekends. These competitions are called "cumulative" contests, and are generally limited to the microwave frequency bands. Short "sprint" contests lasting only a few hours have been popular among contesters that prefer a fast-paced environment, or who cannot devote an entire weekend to a radio contest. A unique feature of the North American Sprint contest is that the operator is required to change frequency after every other contact, introducing another operational skills challenge. Whatever the length of the contest, the top operators are frequently those that can best maintain focus on the tasks of contest operating throughout the event. Some contests, such as the Maine 2 Meter FM Simplex Challenge sponsored by the Wireless Society of Southern Maine, offer newly licensed hams the ability to take part in contesting for the first time, by restricting contacts to a single VHF band, and providing entry categories for anything from a handheld radio to a fully equipped contest station. The wide variety of contests attracts a large variety of contesters and contest stations. The rules and structure of a particular contest can determine the