You can see the divergence above: breath ketones are 16 and 42, so at least double, while BHB = 0.2. Why? No idea.
Since I’m using only my ketonix now (taken usually only in the morning), breath ketones for me seem to indicate how much fat I ate yesterday. If I eat more fat, the value seems to go up. But I haven’t done any exact testing, only know that seems to be the pattern.
Further, if breath ketones go up because of the fat I ate yesterday, what does that mean? I’m not sure it’s meaningful.