title: how accurate is the altitude measurement in mobile phones
body: <p>How accurate is the altitude measurement from a mobile phone's GPS?  I've gathered that the lat/long can vary by hundreds of meters but is that same level of uncertainty present in the altitude values?</p>
  
  <p>In particular I'm working with Windows Phone 7 but I'm sure that this question applies to other mobile devices.  I expect that there are only a few GPS chip manufacturers and the same chip would be used by different phones.</p>
  
  <p>This <a href="https://stackoverflow.com/questions/3272958/gps-coordinates-on-mobile-phones">question</a> deals with how it is calculated but it doesn't mention anything about accuracy or reliability.</p>