Here is the data from my first flight test - ublox is blue, scp1000 is pink. The data was taken while manually flying a SkyFun "pusher jet" in somewhat gusty wind conditions.
There are several things that stand out to me. First is that the scp data is a lot "noisier". Does this actually represent the movement of the aircraft? Perhaps. I cannot really say after this one test.
Second is that the ublox appears to lag badly during fast descents. Seems to keep up going up, but not so much coming down. I suspect this has something to do with the ublox filtering algorithm.
The third thing I see, about which I am the most curious, is that something produced some kind of offset to the pressure at the beginning and end of the flight. If you look closely at the beginning of the graph, you can see that the pressure altitude starts at the same value as the gps altitude (by definition in the software). However, while still on the ground, something causes the pressure altitude to jump down about 22 meters. It bounces back and forth for one period before takeoff. Then at the end of the flight, you can see that the landing altitude is about 22 meters below actual, but then something happens on the ground that causes it to bounce back up around the correct value. This is a real problem. My only theory so far is that putting the canopy on may be trapping some small amount of pressure. However, if this were the case I don't know how the sensor would have the relative level of accuracy it does during the flight. The effect does not appear to be related to airspeed, as the changes noted at the beginning and end were while not in motion.
I also noted that except for the bottom of the "second valley", the effect I noted above, if it is coming and going, could produce the "noise" seen in the pressure altitude. You can see that the peaks of the "noise" correspond fairly well with the gps altitude for much of the flight.
I welcome all thought and comments.....