The other day I noticed the iPhone 6 added a barometer, which apparently a number of Android phones have had for a little while now. The chip is apparently a Bosch BMP280, and is claimed to be reasonably accurate (±1 hPa absolute, and ±0.12 hPa relative).
I’ve always felt some unease with barometric altimeters as a change in the weather or temperature can throw off the numbers. (I.e. I’ll happily take a ±10m GPS vertical error over a ±100m altimeter error.) Having taken a few days to play around with it, I do feel a bit more comfortable with it. I also remain aware that it requires regular “care and feeding”; a day after the last calibration it’s now 40m off. Probably that is from the recent light weather system moving through, which dropped the air pressure about 5 hPa. How it fares in the mountains, with the chance of encountering actual weather in short time frames, remains to be seen.
For apps, I’m using the two shown below; “Pro Altimeter” is a barebones display that can easily be calibrated either manually or via pulling data from nearby airports. “Barometer” has a traditional face, more options, and can capture trends over time. For moving in the mountains I would use the first, and the latter is likely more suitable for home or office use.
For reference, a change of 100m in altitude should generally be indicated by a change of 12 hPa on the barometer (or, 30-43 feet per hPa for most hiking altitudes).
