The altimeter is arguably the most important piece of safety equipment a skydiver wears, more critical even than the parachute itself. While a parachute malfunction can sometimes be managed, losing altitude awareness — not knowing how high you are and how much time you have — transforms a manageable situation into a potentially fatal one within seconds. Every skydiver, from the first AFF student to the most experienced canopy pilot, depends on their altimeter to make decisions that determine whether they live or die.
How Altimeters Work: Barometric vs. GPS
Standard skydiving altimeters use barometric pressure sensors to measure altitude. They work on the principle that atmospheric pressure decreases predictably with increasing altitude — roughly one inch of mercury drop per 1,000 feet of altitude gain in the lower atmosphere. The altimeter's pressure sensor reads the ambient air pressure and converts it to an altitude reading based on a standard atmospheric model.
Barometric altimeters must be calibrated to the correct reference pressure before each jump. The reference pressure — called the altimeter setting — is typically provided by the local airport's weather station or calculated from known field elevation. If the altimeter is set incorrectly, the altitude reading will be systematically wrong throughout the jump. A setting 0.10 inches of mercury low will result in a reading approximately 100 feet higher than actual altitude throughout the jump.
GPS altimeters measure altitude using satellite positioning signals. While GPS altitude can be more accurate in some conditions, it has significant limitations for skydiving. GPS altitude data updates much more slowly than barometric data, making it unsuitable for the rapid altitude changes during freefall. Additionally, GPS signals can be blocked or degraded by interference, canopy fabric, or flight attitudes. Most experienced skydivers consider barometric altimeters the primary instrument and view GPS altitude as supplementary information.
Digital vs. Analog Altimeters
Digital altimeters have become the dominant type in modern skydiving, offering multiple altitude displays, customizable warning settings, and data logging capabilities. A digital altimeter can display current altitude numerically, along with ascent rate, maximum altitude, and multiple user-configurable warnings. Some models integrate with AADs, helmet displays, and audio altitude announcement systems.
Analog altimeters — mechanical instruments with a needle and dial display — remain popular among some experienced skydivers who prefer the immediate visual feedback of a needle position compared to the numerical readout of digital instruments. The argument for analog is that a quick glance at a dial can be processed faster than reading a number, particularly in high-stress situations. The argument against is that digital instruments offer more information and customization. Both types are reliable when properly maintained and calibrated.
Regardless of type, altimeters must be calibrated to the correct altitude before each jump. This means setting the altimeter to read the known field elevation — typically provided by the drop zone — while on the ground, before boarding the aircraft. Many skydivers carry a backup altimeter on the opposite wrist or in a helmet-mounted display, providing redundancy in case of instrument failure.
Proper Placement and Mounting
The placement of your altimeter on your body significantly affects how useful it is during the jump. The most common placement is on the left wrist, mounted on an altimeter band that wraps around the wrist or on the wrist of the hand you use least. During freefall, you should be able to glance at your altimeter with minimal head movement and without disturbing your body position.
Some skydivers prefer a helmet-mounted display — an altimeter display mounted in the helmet's visor area where it is visible without any wrist movement. These are popular among formation skydivers and canopy pilots who need to monitor altitude frequently during complex maneuvers. Helmet displays require proper alignment and must be positioned to avoid interfering with other helmet functions or visibility.
The altimeter should be readable in all lighting conditions. Digital altimeters with backlit displays are preferable for early morning, late evening, and cloud-base jumps where lighting may be poor. Some digital instruments have automatic backlight activation based on ambient light sensor readings. Always verify your altimeter is readable in the specific lighting conditions before every jump.
Developing Automatic Altitude Awareness
The goal for every skydiver is to develop a sense of altitude that supplements but never replaces the altimeter. This sense — sometimes called "altitude awareness" — is a learned skill that develops through hundreds of jumps and involves correlating visual, physical, and auditory cues with altimeter readings. Experienced skydivers often have a surprisingly accurate intuitive sense of their altitude even without looking at an instrument.
Visual cues change dramatically with altitude. The apparent size of familiar objects on the ground, the angular relationship between the horizon and the earth, the color of the sky, and the apparent height of cloud bases all provide altitude information. At very high altitudes, the sky is noticeably darker. At lower altitudes, sounds from the ground become more distinct. These cues become more reliable as you gain experience and consciously correlate them with altimeter readings.
Physical sensations also change with altitude and airspeed. The intensity of the wind blast in freefall, the sound of the airflow, and the sensation of descent rate all provide information about your altitude. Under canopy, the descent rate and ground proximity create distinct sensations that become more intuitive over time. However, these physical cues are not reliable enough to use as primary altitude references — the altimeter is always the definitive source of altitude information.
Altitude Calls and Freefall Communication
In formation skydiving and other group freefall activities, altitude is communicated between jumpers using verbal altitude calls broadcast over radio or communicated through hand signals. Standard altitude calls are made at specific altitudes to coordinate group activities and ensure all participants are aware of critical decision points. Common call altitudes include 9,000 feet for formation break-off planning, 6,000 feet for the final formation approach, 5,500 feet for deployment altitude, and 3,000 feet as a hard no-pull altitude below which no freefall activity is permitted.
Radio altitude communication has revolutionized group skydiving by allowing real-time coordination between jumpers who cannot hear each other over the wind noise. The radio system — typically a small unit mounted in the helmet connected to a headset — allows a designated caller, often the formation organizer or a safety officer, to broadcast altitude calls and instructions to all group members simultaneously.
For solo skydivers, altitude monitoring is an internal discipline. The habit of calling altitude to yourself — "fourteen thousand stable," "twelve thousand turning," and so on — creates an auditory feedback loop that reinforces altitude awareness. This practice should be automatic after the first few jumps, and it should continue throughout your skydiving career regardless of experience level.