In the normal category of my c172, I have a COG range of forward 35.0 aft of datum at 1950lbs or less, with straight line variation to 40.0 inches aft of datum at 2450lbs
The aft range is 47.3 of datum at all weights.
What does this mean.
The datum is the imaginary vertical plane where the horizontal distance is measured.
The ranges above means that my COG that I calculate after doing a weight and balance should fall between that range and those numbers are the maximum and minimum of those limits?