Recently, I've been noticing that the CO2 levels are running somewhat higher than they have been over the last few months.  Checking into the situation with our furnace a bit closer, I notice that it hasn't been running as much over the last week or so, since our outdoor temps have been moderate.  The "bounciness" I've been seeing shows pretty clearly the scheduled blower operation, that is keeping the CO2 levels down against the less-frequent heating cycles.

On another note, I'm going to start work on another module for the SP.  Will be adding an ADC board to allow us to use analog sensors.  Perhaps multi-channel with some input scaling...  Just now starting to think about what it would need.