a topographical map. Skydiving An altimeter is the most important piece of skydiving equipment, after the parachute itself. Altitude awareness is crucial at all times during the jump, and determines the appropriate response to maintain safety. Since altitude awareness is so important in skydiving, there is a wide variety of altimeter designs made specifically for use in the sport, and a non-student skydiver will typically use two or more altimeters in a single jump: Hand, wrist or chest-mounted mechanical analogue visual altimeters. This is the most basic and common type, and is used by (and commonly mandated for) virtually all student skydivers. The common design has a face marked from 0 to 4000 m (or 0 to 12000 ft, mimicking the clock face), on which an arrow points to the current altitude. The face plate sports sections prominently marked with yellow and red respectively, signifying the recommended deployment altitude, as well as emergency procedure decision altitude (commonly known as "hard deck"). A mechanical altimeter has a knob that needs to be manually adjusted to make it point to 0 on the ground before jump, and if the landing spot is not at the same altitude as the takeoff spot, the user needs to adjust it appropriately. Some advanced electronic altimeters are also available which make use of the familiar analogue display, despite internally operating digitally. Digital visual altimeters, mounted on the wrist or hand. This type always operates electronically, and conveys the altitude as a number, rather than a pointer on a dial. Since these altimeters already contain all the electronic circuitry necessary for altitude calculation, they are commonly equipped with auxiliary functions such as electronic logbook, real-time jump profile replay, speed indication, simulator mode for use in ground training, etc. An electronic altimeter is activated on the ground before the jump, and calibrates automatically to point to 0. It is thus essential that the user not turn it on earlier than necessary to avoid, for example, the drive to a dropzone located at a different altitude than one's home which could cause a potentially fatal false reading. If the intended landing zone is at a different elevation than the takeoff point, the user needs to input the appropriate offset by using a designated function. Audible altimeters (also known as "dytters", a genericised trademark of the first such product on the market). These are inserted into one's helmet, and emit