I got DEXA (dual energy x-ray absorptiometry) tests done, three over the course of a year. During that year, I gained about 4 pounds of muscle and lost about 6 pounds of fat, for a scale loss of 2 pounds. Contrast that with when I do a fast > 24 hours, where I can lose (or gain) 5 pounds in a single day. So, I stopped using the scale. I now just use clothes, particularly pants.
As for taking ketones, I have thousands of ketone and blood sugar samples. I still use my ketonix, but just because I keep it at work. Today, it registered a 67 (first generation Ketonix), which is shockingly high. I think that’s because I fasted Monday, worked out Tuesday morning, then ate a ton Tuesday, a lot of which was fatty. I typically eat higher protein, but just happened to buy smoked kielbasa over the weekend, so ate a lot of that. I think the Ketonix is simply registering extra fat I have available from eating a lot of fat, which is why I’ve switched to higher protein (hoping to get the fat from my body instead of my food). Eating higher protein, my ketonix is always much lower, in the 20-30 range. I have stopped using blood ketones (and stopped pee ketone testing years ago) and blood sugar, though if I could afford the $75/month for my Free Style Libre continuous glucose monitor, I would get that. It tells you stuff nothing else can.