If you're evaluating the accuracy of Elevation Tracker's data, please consider a few facts about GPS technology:

  1. Margin of error: Elevation Tracker uses elevation data provided by your iPhone's GPS receiver. GPS (Global Positioning System) was designed to find an object's latitude and longitude, and is generally accurate to about 10 meters for that purpose. It can also be used to locate an object's elevation above sea level, but is only accurate to about 30 meters for that purpose. Consequently, the elevation displayed by Elevation Tracker is likely to be off by around 30 meters at any given moment. This is why a trip that starts and ends at the same location might show a different starting and ending elevation, or why the displayed elevation might change while you are standing still.
  2. Data smoothing: Since your phone provides GPS data to apps running on it, any other location-related apps you use are probably working with the same data. But they might show different results because each app uses its own algorithm for smoothing the data. Data smoothing is a process of analyzing the fluctuations in GPS data to try and estimate the "true" values. Elevation Tracker applies a simple, 60-second moving average to incoming elevation data, which provides results that are comparable, but not exactly equal, to other apps.
  3. Real world use: The best way to test Elevation Tracker is to use it in the activities it was designed for, like running, biking or hiking. Beware of tests that do not resemble real-world use, such as a test performed indoors (GPS accuracy is much worse indoors) or over a very small distance (such as walking up a flight of stairs).

The bottom line is that no GPS-based elevation tool will be perfectly accurate, but the smoothed data collected during the course of your activities should provide very useful info for measuring the amount of climbing you are doing.