Stratologgeraltitude question

I've been using the Perfectflite Stratologger for a while now and really have had great success. The only issue is that when I read the data on my PC, it always shows the altitude on the pad as anywhere from -171 feet, to -257 feet. Is this normal and is the max altitude that amount off? Is there a way to zero the altimeter on the pad?

Thanks for any help!

IF your launch site is near sea level, it may read negative.

Atmospheric conditions vary causing it to be a +/- 200 ft or so...

If not then, it maybe out of calibration?


JD

Thanks JD...that's what I suspected, and my remaining question is, does my peak altitude remain 1,100 feet, or do I add the -271 to it for a true peak altitude of1,371 feet?

What you are seeing is the first pressure reading which is proportional to the absolute atmospheric pressure assuming the standard pressure of 29.92" Hg at sea level. The real sea level pressure varies by +/-1" due to weather and this is used to normalize the calculation to AGL based on the US Standard Atmosphere Model. All measurements after that are reported as AGL. It's all described in the manual.

Bob

Thank you Bob...That makes sense. SO my peak altitude shown in the data download, truly is the AGL for that day and that flight.