The best look inside of the body so far as been blood meter - currently using this one:
https://keto-mojo.com/ Recommended by Rob here - least expensive strips at $1 each - see my journal back a few weeks as I tested breath, urine, blood BHB and Glucose head to head.
Currently i'm seeing what it takes to maintain "optimal" from diet only 1.5-3mmol/L I think this is going to be easily accomplished at 20 net carb and M-W-F ADF at 36hr - It's really interesting to see how refeed affects numbers - I'll also experiment with protein vs fat for cals after I stabilize on the ADF plan in a week or two.
Here's tracking this month so far - started with fast on Monday
April 2020
BHB = Beta HydroxyButyrate, Glu = Glucose
Ux = Urine Strips, Nc = Net Carb
Lbs = English Pounds, Act = (Type-Intensity[1-10])
Date - BHB - Glu - Ux - Nc - Lbs - Act
0401 - 0.9 - 101 - 15 - 00 - 213 - KiteFoil-7
0402 - 3.1 - 076 - 40 - 17 - 209 - KiteFoil-7
0403 - 1.2 - 101 - 30 - 00 - 213 - None
0404 - 3.2 - 074 - 40 - 10 - 208 -
Look back here at end for March experimentation:
http://downhaul.com/lowcarb/daily.txt
Have fun Barb, poke your finger!