I noticed the same thing and contacted Cris about it. Here is my question and his answer below:
I had a question regarding the ASL Altitude readout. Both units are showing values between -72 and -55 when the page refreshes. I know that my house is 134ft ASL. Why is there such a error in both units and within the same range? I disconnected and reconnected my phone’s wifi to each after each sat on my bench powered by my bench power supply. I had assumed that it would eventually settle out after a few minutes of sampling , but they didn’t. Is anything wrong? I have attached screen shots, one from each of my Quantums.
Here is his reply:
Brad:
The ASL altitude is dependent on temperature, and the temperature sensors take awhile to settle down... maybe 30 minutes. What's really more important is the relative AGL altitude during flight... and that's pretty much independent of what ground altitude it shows.
The ASL altitude gets updated over time after arming, so it tends to be more accurate during actual launch conditions. When it's not armed, what you're seeing is the last reading, with no filtering. That's why it might vary, and it will be more accurate outdoors than indoors.
Cris
After a couple days I powered my Quantums up again and things were close to normal.
Brad