After a bunch of file format manipulation, I plotted altitude (AGL) vs. time from an altimeter along with GPS. The altimeter is PerfectFlite MAWD, and the GPS is Big Red Bee 900. Both are several years old and not on the cutting edge of technology. I am quite pleased with the agreement. Data was collected from the BRB900 in two ways. One was the recording on the onboard flash memory of the transmitter. The second was to connect the LCD receiver to a com port and interface with u-center software for real-time NMEA recording during flight. u-center is nifty freeware for all kinds of plotting and analysis, making for a decent poor-man's telemetry link. It is fun to replay the data stream after the flight. This pic shows the rocket landing in a woodlot. (It was recovered from the top of a 40 ft tree.) Here are the altitude comparisons. The BRB900 transmitter lost GPS lock for the first 12 seconds of flight. The base station receiver lost signal for the first minute or so. The apogee recordings agree to about 700 ft. All my OR simulation variations bracket these values, too. Pretty good. Interestingly, the recordings differ the most at high altitude and are very close at low altitude. I am wondering if the lack of temperature correction on the MAWD may be understating the altitude. It was a hot, 85 deg F day, far warmer than the standard atmosphere model.