I use my quad for aerial videography of kiteboarders. My main mode of operation usually involves using alt-hold (and more recently loiter) to set an altitude just beyond the reach of the kites (~30m above the water level) This allows me to better focus on getting the shot I want while having some assurance that I am not going to hit anything. My rig has a usable flight time of around 20 minutes and over the course of one flight I can see an altitude error of over 10m in certain conditions due to fluctuations in barometric pressure. This means that although alt-hold is still a useful feature, I can not rely on it to any degree and must always keep an eye on how it is performing. I use Droidplanner on my Galaxy S4 attached to my transmitter connected via 433Mhz wireless. It occurred to me that many modern phones have an accurate barometer and that a setup such as mine should be able to transmit barometric corrections to the aircraft. As long as the operator is not changing altitude, the barometric pressure as measured by the phone can be monitored and any changes used to correct drift on the aircraft. I was wondering if anyone has considered this and if absolute altitude accuracy was an issue for anyone else?