Field Manual
Altim-O-Tron 1.0 · iPhone
Most questions about an altimeter are really questions about physics. Here are the ones that come up most — and a real address to write to if yours isn't listed.
Common questions
My altitude doesn't match my GPS watch / the trail sign.
They're probably measuring different things. Trail signs and maps usually quote elevation above the geoid (mean sea level), while raw GPS reports height above an ellipsoid — a smooth mathematical earth that can differ from real sea level by well over 100 feet depending on where you're standing. Altim-O-Tron blends GPS with the barometer and reports the figure that matches maps.
Give it a minute with a clear view of the sky. The ± figure under the readout is the app telling you honestly how confident it is.
Does it work in airplane mode?
Yes. GPS reception is a receiver, not a connection — the satellites broadcast whether or not you're paying a carrier. Airplane mode does switch off the GPS radio on iPhone, so turn Location Services back on (airplane mode + location enabled is a valid combination) and the app works with no cellular or Wi-Fi at all. The barometer never needed a signal in the first place.
The compass is wandering or pointing somewhere absurd.
Magnetometers get confused by metal and magnets — car dashboards, camera tripods, and above all the magnets in cases and MagSafe accessories. Step away from the metal, take the phone out of the case, and move it in a figure-eight for a few seconds to recalibrate.
The accuracy tile shows the current heading uncertainty. If it stays high, something nearby is magnetic.
Can it record with the screen locked?
Yes. Start a session from the Log tab, then pocket the phone — recording continues with the screen off. For this to work, allow location access "Always" (or at minimum "While Using the App", which iOS extends to a locked screen during an active session) in Settings › Privacy › Location Services › Altim-O-Tron.
How do I get my track into another app?
Open a saved session and use the share button to export it as a GPX file — a plain standard format that Gaia, CalTopo, Strava, Garmin, and most mapping software read directly. Send it wherever you like via AirDrop, Files, or email. The app doesn't upload it anywhere.
Why does pressure altitude differ from my altitude?
Pressure altitude is what an aircraft altimeter reads with its setting at the standard 1013.25 hPa. It's a useful aviation figure, but on any day that isn't meteorologically average it won't match your true elevation. The big number on the dial is the real one.
The weather graph is empty or has gaps.
The barograph logs pressure while the app is open, so a fresh install has nothing to plot yet and long stretches with the app closed show as gaps. Open it now and then over a couple of days and the 48-hour trace fills in. The three-hour tendency needs at least three hours of samples before it will commit to an opinion.
What is a smoot, and why is it an option?
A smoot is 5 feet 7 inches — the height of Oliver Smoot, who in 1958 was repeatedly laid end over end across Harvard Bridge by his fraternity to measure it. The markings are still repainted today. Giraffes, fathoms, and furlongs are offered in the same spirit.
Which iPhones are supported?
Any iPhone with a barometer, which means iPhone 6 and later. Without one the app still works from GPS alone, but loses the fast response and the weather features.
Still stuck?
Write with your iPhone model, iOS version, and what you saw versus what you expected. Screenshots help enormously. There's no ticket system and no bot — it's a small operation, and messages get read.