Ignore the descriptive blurbs above the numbers. They’re designed to encourage Joe and Jill SAD dieter they’re eating more or less carbs, but for us they’re meaningless. We know we’re burning fat. And in your case probably undetectable carb. In my case, I might have detectable carb burn since I’m eating non-zero amounts.
More importantly for us, is whether or not it’s useless, assuming it’s actually measuring changes within a very narrow range of RER values. Without displaying the actual calculated RER value, I think it’s not very useful. In your case, because you calibrated a very narrow range of min/max values it might be useless, especially considering T2D adding complexity to your situation.
However, instead of getting discouraged because you’re blowing numbers you don’t expect, I’d suggest trying to determine why you’re blowing different numbers at different times and circumstances. That might be useful. If it turns out that the Lumen values returned are totally random over the course of a couple of weeks, then I think it would be safe to conclude the device is useless.
In my case, I’m using my Ketonix to try to determine if there is any correlation between BrAce and Lumen numbers that might be useful. So I’m reserving judgement until I can conclude one way or the other.
BTW, I just blew another Lumen 1. I had my regular morning liter of keto coffee between 5:30-6:00am, worked a 5 hour shift from 7-12, did some shopping afterwards. Took the sample immediately when I got home (1:30pm). So have not eaten anything since 6am. Surprisingly, BrAce was relatively low 9.6 ppm. The final 2-3 hours were quite busy and I suspect I was burning mostly FA. So if I was generating significant acetoacetate, it was either being utilized directly along with the FA and/or converted to/from β-hydroxybutyrate and not a whole lot disintegrating into acetone and CO2.