It’s still good for gross measures. Say, your GKI goes down (or at least I think GKI going down is better), that’s probably true. It’s just if you wanted to know an exact number, that’s probably not going to happen.
It’s like CGMs or the scale or similar: better for trends than exact numbers.
You might ask yourself, Bob, if these are poor at exact values, why do you use them? I want to test some things, and I would use them as gross measures of what’s going on. So, if I go from high protein to high fat, and my ketone go from say 0.5 consistently to 1.0 consistently, this would be a trend. It’s if the values don’t change or are varying even after changing diet that would be an issue.