Glad the logging issue seems to be sorted, sorry it gave you some trouble for a while.
There’s some odd fields in the data file: RMS INT Temp[C]
comes out at -271.53062, oddly close to absolute zero (maybe the AC temperature component expressed in Kelvin?), but otherwise it works.
You’re exactly right. Internally the mooshimeter fills a sample buffer, calculates the average and the RMS, and sends all of that data back over the air to the smartphone. The smartphone decides what to display. When logging, it’s easiest in firmware to just write all of it to the SD card. Since the temperature has almost no AC component, that’s recorded as zero, which when you feed it through the formula to convert temp. sensor volts to degrees C, ends up being almost absolute zero.
I hope the O2 sensing experiment works well! If you write about it somewhere please send a link, I’d love to see it.