The online BMI calculators are not notoriously inaccurate. Not as good as immersion or calipers, but not so bad.
did you mean lean body mass? BMI is a kg/m^2 there is not other way to measure it because it doesn't measure anything but the ratio of your weight to the square of your height. The charts are completely accurate because it is what it is. It is not a measure of body fat and you cannot measure your BMI with calipers.
I'll tell you what to do with these numbers. Nothing.
It's grandma, but you can call me sir.