How much did you climb?

Three taps a session

1. Tap StartBefore a walk, a hike or a flight of stairs.
2. WalkAscent and descent add up every second, with the climb also shown as stair-equivalents.
3. Tap StopThe session lands in History with its altitude profile, to scroll back through later.

What it looks like

How an iPhone measures height without GPS

Air pressure falls as you go up — near sea level by roughly one hectopascal for every eight metres. Your iPhone has a barometer sensitive enough to notice a flight of stairs, and it works where GPS does not: in stairwells, car parks, lifts and tall buildings.

Weather moves the pressure too, slowly. So a barometer is excellent at how much you climbed in the next hour and poor at your exact height above the sea. That is why AltLog counts climb and descent instead of claiming an elevation.

"What is my altitude above sea level?"

AltLog does not answer that one, on purpose — a barometer alone cannot do it reliably. For height above sea level use a map app or anything with GPS. For how many metres you gained on today's walk, use AltLog.

Honest about the limits

• Relative, not absolute. It measures change from where you pressed Start, not your elevation.
• Anywhere there is air. A sealed, pressurised cabin — an aircraft — defeats any barometer.
• Not a safety instrument. Do not navigate mountains or aircraft by it.
• No account, no location. Pressure samples and sessions stay on your iPhone.

Get AltLog on the App Store