Your Altimeter's Lifeline: The Ultimate Maintenance & Calibration Guide

In skydiving, your altimeter isn't just another piece of gear---it's your primary link to the ground, your ultimate decision-making tool, and the device that stands between a routine jump and an emergency. A malfunctioning or poorly calibrated altimeter is a risk no responsible jumper should ever take. Treating it with the same reverence as your main canopy is non-negotiable. This guide outlines the essential maintenance schedule and calibration practices to keep your altimeter performing flawlessly, jump after jump.

Why Maintenance Isn't Optional: The Stakes

An altimeter failure or inaccuracy can lead to:

• Low or high pulls: The most critical risk, potentially leading to canopy collisions or ground impact.
• Poor pattern flying: Misjudging your altitude over the landing area, leading to off-field landings or obstacles.
• False confidence: Believing you're higher or lower than you actually are during critical phases of flight.

Your altimeter is a precision mechanical or electronic instrument. It endures shock, vibration, pressure changes, and environmental exposure. Without a strict care regimen, its accuracy will drift.

The Golden Rule: The Pre-Jump Check (Every Single Jump)

This is your non-negotiable, first-line defense. Perform this before every single jump, without exception.

1. Visual Inspection:

   • Case & Lens: Check for cracks, deep scratches, or moisture/fogging inside the lens. Any compromise to the seal is a red flag.
   • Strap & Mount: Ensure the wrist strap or mount is intact, with no fraying or broken components. Verify it's securely attached to your wrist or gear.
   • Battery Compartment: Look for signs of corrosion or leaking batteries.

2. Functional Test (The "Tap & Listen"):

   • Analog (Dial) Altimeters: Gently tap the casing. The needle should move freely and return smoothly to its resting position (usually zero on the ground). Listen for any ticking, grinding, or sticky sounds---signs of internal wear or debris.
   • Digital/Audible Altimeters: Power it on. The display should illuminate clearly. Test the audible alarm (if equipped) at a low setting to confirm it sounds.

3. Zero Verification:

   • On the ground, at your exit altitude (field elevation), your altimeter must read the correct field elevation. If you're at a dropzone at 1,500 ft MSL, your altimeter should read 1,500 ft (or 0 ft AGL if set to zero). If it does not, do not jump. Send it for service immediately.

The Scheduled Maintenance Calendar

Daily / Weekly (User Level)

• Post-Jump Wipe Down: After jumping, gently wipe the exterior with a clean, dry cloth to remove dirt, sweat, and moisture. Pay attention to the seal around the lens.
• Battery Check: For digital units, check battery life regularly. Replace batteries proactively---don't wait for a low battery warning. For analog units, ensure the crown (winding knob) is screwed down tightly if it has a screw-down crown.
• Storage: Store in a cool, dry place, away from direct sunlight and extreme temperatures. Avoid leaving it in a hot car. Use a padded case if available.

Monthly (Detailed User Inspection)

• Deep Clean: Using a soft brush (like a clean makeup brush or paintbrush), gently clean around the bezel and any crevices to remove packed dirt or sand that could affect the mechanism.
• Seal Check: Inspect the rubber or silicone gasket/seal around the lens for signs of wear, cracking, or flattening. A compromised seal is the #1 cause of internal moisture and failure.
• Strap Integrity: Thoroughly examine the strap, stitching, and Velcro for wear.

Every 6 Months (Professional Service Recommended)

This is the critical interval for a full professional inspection and calibration. Do not skip this.

• What the Pro Does:
  • Complete Disassembly: Opens the case in a controlled environment.
  • Internal Cleaning: Uses specialized solutions to remove old lubricants and microscopic debris from the movement.
  • Movement Inspection: Checks for wear on gears, pivots, and the aneroid capsule (in analog units).
  • Pressure Testing: Places the altimeter in a calibrated pressure chamber to verify its accuracy across its entire range.
  • Calibration Adjustment: Precisely adjusts the mechanism to match known pressure standards.
  • Seal Replacement: Replaces the case gasket to ensure water and dust resistance.
  • Battery Test: Checks battery contacts and power draw (for electronics).
  • Final Certification: Some shops provide a calibration certificate.

After Any Significant Event

• Impact: If you drop your altimeter hard, hit it against the aircraft door, or experience a hard opening, get it checked immediately---even if it seems to work.
• Water Exposure: If it gets submerged or heavily soaked (even if it's "water-resistant"), it must be serviced. Moisture is the enemy.
• Suspicious Readings: Any time you get an altitude reading that conflicts with your visual references (e.g., you're clearly over the landing pattern but it reads 4,000 ft), ground it and send it for service.

Calibration Demystified: Tips & Best Practices

Calibration is the process of adjusting your altimeter to read the correct pressure (altitude). It's a precise task best left to professionals, but you must understand the principles.

1. Know Your Setting: Understand the difference between Absolute Altitude (height above sea level) and Indicated Altitude (height above ground level). Most altimeters are set to read field elevation on the ground (0 ft AGL). Some competition or special-use altimeters are set to absolute altitude. Know which yours is and never change it without a specific reason and full understanding.
2. The Ground Zero is Sacred: The most fundamental calibration point is at the dropzone. Your altimeter must match the known field elevation when on the ground. Use the dropzone's published elevation (often found on the windsock or pilot's info). If it's off by more than 10-20 feet, it needs service.
3. Temperature Matters: Extreme cold can cause minor, temporary inaccuracies in some analog altimeters. This is usually not a calibration issue but a known physical effect. If you jump in sub-zero conditions, be aware and trust your eyes and experience more.
4. Never "Calibrate" Mid-Season: Do not adjust the calibration screw yourself based on a single jump's perception. Your perception can be wrong (e.g., misjudging the landing pattern). Trust the instrument, but only if it's known to be accurate from a recent professional service.
5. Use a Known Reference: If you have access to a second, recently serviced, and verified altimeter (from a friend or instructor), you can do a "side-by-side" check on the ground and in the plane. They should read virtually identical. This is a great cross-check before a big jump or after your own service.

The "Do Not" List: Altimeter Suicide

• DO NOT open the case yourself unless you are a certified watchmaker/altimeter technician.
• DO NOT attempt to adjust the calibration screw with a screwdriver unless you have a calibrated pressure source and know exactly what you're doing.
• DO NOT ignore a sticky needle, fuzzy digital display, or alarm that sounds at the wrong time.
• DO NOT use an altimeter that has been dropped, hit, or submerged without professional inspection.
• DO NOT assume a new altimeter is perfectly calibrated out of the box. Always verify its ground reading against the known field elevation.

The Bottom Line: A Culture of Care

Your altimeter maintenance schedule should be as ingrained as your pull sequence. Think of it this way:

Investing in regular, professional maintenance is the cheapest insurance policy you can buy in this sport. It costs a fraction of a new altimeter and provides priceless peace of mind. When your altimeter is trustworthy, you can focus on what really matters: flying your body, flying your canopy, and enjoying the incredible journey down.

Your life depends on a number on a dial. Keep it honest.