page_title: Altimeter
section_title: Skydiving
hierarchical_section_title: Altimeter / Pressure altimeter / Skydiving
caption_attribution_description: English: Skydiver in free fall, making use of a hand-mounted altimeter. The analogue face is visible, showing colour-coded decision altitudes. The depicted altimeter is electronic, despite using an analogue display.Polski: Skoczek spadochronowy używa wysokościomierza w swobodnym spadku. Widoczna jest analogowa tarcza z kolorami oznaczającymi krytyczne wysokości. Wysokościomierz na zdjęciu to model elektroniczny, pomimo użycia analogowego cyferblatu.Dansk: En faldskærmspringer bruger sin højdemåler i frit fald. Man kan se analogskiven med vigtige højder markerede med farver. Den viste højdemåler er elektronisk, selv om den bruger analogvisning.
context_page_description: An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. The most common unit for altimeter calibration worldwide is hectopascals, except for North America and Japan where inches of mercury are used. To obtain an accurate altitude reading in either feet or meters, the local barometric pressure must be calibrated correctly.
context_section_description: 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 a warning tone at a predefined altitude. Contemporary audibles have evolved significantly from their crude beginnings, and sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched quickly, electronic logbook with data transfer to a PC for later analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are strictly auxiliary devices, and do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness. The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, and virtually all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and often banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves.
  Auxiliary visual altimeters. These do not show the precise altitude, but rather help maintain a general indicator in one's peripheral vision. They might either operate in tandem with an audible equipped with an appropriate port, in which case they emit warning flashes complementing the audible tones, or be standalone and use another display mode, such as showing either green or red light depending on the altitude.
  Speaking altimeters (also known as voice altimeters). Another type of altimeter that combines both audible and visual altimeter functions. Unit has all necessary altitud
caption: Skydiver in free fall, making use of a hand-mounted altimeter. The analogue face is visible, showing colour-coded decision altitudes. The depicted altimeter is electronic, despite using an analogue display.
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