Support the mast with the tip at a height which will allow the tip of the mast not to hit the ground when the weight is placed on it. Fix in place at the butt to allow to rest on the collar as it holds by the mast step and deck of the boat. Mark the point A. See picture below.
Place the weight (12 kg Sideways / Fore & Aft) on the tip of the mast at the measurement band. Mark the point B for sideways and fore&aft.
Take a taught string from the top of the bottom measurement band (D) to the bottom of the top one (C).
Measure the distance in millimeters between the string and the mast (Sideways and Fore&Aft) in every 1/4 of the distance CD.