I did draw the control chart, and thermostat B is definitely under statistical process control: https://xkqr.org/info/xmr.html?baseline=33,97,41,65,72,71,64...
If someone wants to learn more, this is how I put the introduction: https://entropicthoughts.com/statistical-process-control-a-p...
Almost nothing has (effectively) unbounded variance, so most things are under statistical control in a sense. With some notable exceptions (earthquakes, any other event with exponentially decreasing frequency and exponentially increasing damage).
For the sake of argument I assumed the author meant that the variance of the thermostat was too high to be practical.
My expectation is that Lorin would read the parent comment and say some variant of "oh, whoops, I didn't check." As the parent noted, it's not really that important to the overall point.
Yes, the variability of the thermostat is awful, and the SPC practitioner would care about that. But the key thing is that dealing with bad variation that's in control requires different techniques than dealing with actual out-of-control processes.
Especially older buildings where things like uneven sun loading have a bigger impact, and where things like outdoor reset are less common.