Thank you for the help, I did a search and I found out there could be a 20% error because of the water. I'm following a keto diet, so that's why when I eat a lot (carbs) the BF goes down. I did order a plicometer.
This value for me is necessary only for my motivation

It's not a good thing to be in diet for months, loose some weight and read the BF is alwais the same.