All features / Recording
Elevation
you can trust.
GPS is terrible at altitude. The horizontal fix is great; the vertical can be off by 30 feet on a good day and 100 feet under cover. PeakPulse fuses the barometer in your iPhone and Apple Watch with GPS so your climb gain is right — even in tunnels, deep canopy, and slot canyons.
Why GPS elevation lies
A GPS receiver triangulates position from satellites overhead. Horizontal accuracy is excellent — usually within a few meters. Vertical accuracy is much worse, because the geometry favors horizontal fix and the satellites you can see are constrained to the sky above you.
The result: GPS-only elevation drifts. You climb a 1,500-foot hill and your app says you climbed 1,700 (or 1,300). On switchbacks, the drift compounds. Under trees, GPS can lose lock entirely and the elevation line goes flat for minutes at a time — which is why your "total ascent" on some apps undershoots by hundreds of feet.
The barometer in your phone is sensitive enough to feel an elevator move one floor. Your trail run has more vertical change than a building.
How fusion works
PeakPulse uses two sensors together because each has weaknesses the other doesn't share.
-
01
The barometer measures pressure change
As you climb, atmospheric pressure drops. The pressure sensors in iPhone 6+ and Apple Watch are accurate to fractions of a hectopascal — that's roughly one foot of vertical resolution. Pressure doesn't care about trees or tunnels.
-
02
GPS provides the absolute reference
The barometer is great at relative change but it drifts with weather. PeakPulse uses GPS to anchor the absolute altitude when GPS confidence is high, then trusts the barometer for the moment-to-moment changes.
-
03
Outlier filtering removes spikes
A single bad point — wind gust hitting the pressure port, momentary GPS jump — gets smoothed out by the fusion model. You see the real elevation profile, not the sensor noise.
-
04
Weather drift correction over long efforts
On a multi-hour effort, weather pressure can shift by several hectopascals as a front rolls through. PeakPulse periodically realigns against trusted GPS samples so a passing storm doesn't appear as 300 feet of phantom climb.
Where it matters most
Common questions
Which devices have a barometer?
Every iPhone since iPhone 6 (2014) and every Apple Watch since Series 3 (2017). If your device is newer than that, fusion is on. On older devices PeakPulse falls back to GPS-only elevation — still accurate horizontally, less so vertically.
Does this affect battery life?
Barely. The barometer is a low-power sensor — it's already running for things like Apple's stairs-climbed metric. Adding fusion to PeakPulse is a math cost, not a power cost.
Will pressure changes from weather throw off my climb gain?
Short answer: no, because PeakPulse continually realigns against GPS. Long answer: a typical weather front shifts pressure by 3-5 hectopascals over hours, which would be ~80-130 feet of error if uncorrected. The fusion model recognizes slow pressure drifts and corrects them against GPS samples whenever GPS confidence is high.
Can I see vertical accuracy in real time?
Yes. The recording screen has an optional "elevation accuracy" data field that shows the current confidence interval. Most of the time you'll see ±2-5 meters; in challenging conditions it widens.
What if there's a rogue elevation point in my track?
The fusion filter catches most outliers automatically. For the rare survivor, the Route Editor lets you remove individual points — your elevation profile and climb gain recompute instantly.